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POSTCONF(5)                   File Formats Manual                  POSTCONF(5)



NAME
       postconf - Postfix configuration parameters

SYNOPSIS
       postconf parameter ...

       postconf -e "parameter=value" ...

DESCRIPTION
       The Postfix main.cf configuration file specifies a small subset of all
       the parameters that control the operation of the Postfix mail system.
       Parameters not specified in main.cf are left at their default values.

       The general format of the main.cf file is as follows:

       o      Each logical line has the form "parameter = value".  Whitespace
              around the "=" is ignored, as is whitespace at the end of a
              logical line.

       o      Empty lines and whitespace-only lines are ignored, as are lines
              whose first non-whitespace character is a `#'.

       o      A logical line starts with non-whitespace text. A line that
              starts with whitespace continues a logical line.

       o      A parameter value may refer to other parameters.

              o      The expressions "$name", "${name}" or "$(name)" are
                     recursively replaced by the value of the named parameter.

              o      The expression "${name?value}" expands to "value" when
                     "$name" is non-empty. This form is supported with Postfix
                     version 2.2 and later.

              o      The expression "${name:value}" expands to "value" when
                     "$name" is empty. This form is supported with Postfix
                     version 2.2 and later.

              o      Specify "$$" to produce a single "$" character.

       o      When the same parameter is defined multiple times, only the last
              instance is remembered.

       o      Otherwise, the order of main.cf parameter definitions does not
              matter.

       The remainder of this document is a description of all Postfix
       configuration parameters. Default values are shown after the parameter
       name in parentheses, and can be looked up with the "postconf -d"
       command.

       Note: this is not an invitation to make changes to Postfix
       configuration parameters. Unnecessary changes can impair the operation
       of the mail system.

2bounce_notice_recipient (default: postmaster)
       The recipient of undeliverable mail that cannot be returned to the
       sender.  This feature is enabled with the notify_classes parameter.

access_map_defer_code (default: 450)
       The numerical Postfix SMTP server response code for an access(5) map
       "defer" action, including "defer_if_permit" or "defer_if_reject". Prior
       to Postfix 2.6, the response is hard-coded as "450".

       Do not change this unless you have a complete understanding of RFC
       2821.

       This feature is available in Postfix 2.6 and later.

access_map_reject_code (default: 554)
       The numerical Postfix SMTP server response code for an access(5) map
       "reject" action.

       Do not change this unless you have a complete understanding of RFC
       2821.

address_verify_cache_cleanup_interval (default: 12h)
       The amount of time between verify(8) address verification database
       cleanup runs. This feature requires that the database supports the
       "delete" and "sequence" operators.  Specify a zero interval to disable
       database cleanup.

       After each database cleanup run, the verify(8) daemon logs the number
       of entries that were retained and dropped. A cleanup run is logged as
       "partial" when the daemon terminates early after "postfix reload",
       "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.7.

address_verify_default_transport (default: $default_transport)
       Overrides the default_transport parameter setting for address
       verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_local_transport (default: $local_transport)
       Overrides the local_transport parameter setting for address
       verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_map (default: see postconf -d output)
       Lookup table for persistent address verification status storage.  The
       table is maintained by the verify(8) service, and is opened before the
       process releases privileges.

       The lookup table is persistent by default (Postfix 2.7 and later).
       Specify an empty table name to keep the information in volatile memory
       which is lost after "postfix reload" or "postfix stop". This is the
       default with Postfix version 2.6 and earlier.

       Specify a location in a file system that will not fill up. If the
       database becomes corrupted, the world comes to an end. To recover
       delete (NOT: truncate) the file and do "postfix reload".

       Postfix daemon processes do not use root privileges when opening this
       file (Postfix 2.5 and later).  The file must therefore be stored under
       a Postfix-owned directory such as the data_directory.  As a migration
       aid, an attempt to open the file under a non-Postfix directory is
       redirected to the Postfix-owned data_directory, and a warning is
       logged.

       Examples:

       address_verify_map = hash:/var/db/postfix/verify
       address_verify_map = btree:/var/db/postfix/verify

       This feature is available in Postfix 2.1 and later.

address_verify_negative_cache (default: yes)
       Enable caching of failed address verification probe results.  When this
       feature is enabled, the cache may pollute quickly with garbage.  When
       this feature is disabled, Postfix will generate an address probe for
       every lookup.

       This feature is available in Postfix 2.1 and later.

address_verify_negative_expire_time (default: 3d)
       The time after which a failed probe expires from the address
       verification cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_negative_refresh_time (default: 3h)
       The time after which a failed address verification probe needs to be
       refreshed.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_poll_count (default: normal: 3, overload: 1)
       How many times to query the verify(8) service for the completion of an
       address verification request in progress.

       By default, the Postfix SMTP server polls the verify(8) service up to
       three times under non-overload conditions, and only once when under
       overload.  With Postfix version 2.5 and earlier, the SMTP server always
       polls the verify(8) service up to three times by default.

       Specify 1 to implement a crude form of greylisting, that is, always
       defer the first delivery request for a new address.

       Examples:

       # Postfix <= 2.6 default
       address_verify_poll_count = 3
       # Poor man's greylisting
       address_verify_poll_count = 1

       This feature is available in Postfix 2.1 and later.

address_verify_poll_delay (default: 3s)
       The delay between queries for the completion of an address verification
       request in progress.

       The default polling delay is 3 seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_expire_time (default: 31d)
       The time after which a successful probe expires from the address
       verification cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_refresh_time (default: 7d)
       The time after which a successful address verification probe needs to
       be refreshed.  The address verification status is not updated when the
       probe fails (optimistic caching).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_relay_transport (default: $relay_transport)
       Overrides the relay_transport parameter setting for address
       verification probes.

       This feature is available in Postfix 2.1 and later.

address_verify_relayhost (default: $relayhost)
       Overrides the relayhost parameter setting for address verification
       probes. This information can be overruled with the transport(5) table.

       This feature is available in Postfix 2.1 and later.

address_verify_sender (default: $double_bounce_sender)
       The sender address to use in address verification probes; prior to
       Postfix 2.5 the default was "postmaster". To avoid problems with
       address probes that are sent in response to address probes, the Postfix
       SMTP server excludes the probe sender address from all SMTPD access
       blocks.

       Specify an empty value (address_verify_sender =) or <> if you want to
       use the null sender address. Beware, some sites reject mail from <>,
       even though RFCs require that such addresses be accepted.

       Examples:

       address_verify_sender = <>
       address_verify_sender = postmasterATmy.domain

       This feature is available in Postfix 2.1 and later.

address_verify_sender_dependent_default_transport_maps (default:
$sender_dependent_default_transport_maps)
       Overrides the sender_dependent_default_transport_maps parameter setting
       for address verification probes.

       This feature is available in Postfix 2.7 and later.

address_verify_sender_dependent_relayhost_maps (default:
$sender_dependent_relayhost_maps)
       Overrides the sender_dependent_relayhost_maps parameter setting for
       address verification probes.

       This feature is available in Postfix 2.3 and later.

address_verify_service_name (default: verify)
       The name of the verify(8) address verification service. This service
       maintains the status of sender and/or recipient address verification
       probes, and generates probes on request by other Postfix processes.

address_verify_transport_maps (default: $transport_maps)
       Overrides the transport_maps parameter setting for address verification
       probes.

       This feature is available in Postfix 2.1 and later.

address_verify_virtual_transport (default: $virtual_transport)
       Overrides the virtual_transport parameter setting for address
       verification probes.

       This feature is available in Postfix 2.1 and later.

alias_database (default: see postconf -d output)
       The alias databases for local(8) delivery that are updated with
       "newaliases" or with "sendmail -bi".

       This is a separate configuration parameter because not all the tables
       specified with $alias_maps have to be local files.

       Examples:

       alias_database = hash:/etc/aliases
       alias_database = hash:/etc/mail/aliases

alias_maps (default: see postconf -d output)
       The alias databases that are used for local(8) delivery. See aliases(5)
       for syntax details.

       The default list is system dependent.  On systems with NIS, the default
       is to search the local alias database, then the NIS alias database.

       If you change the alias database, run "postalias /etc/aliases" (or
       wherever your system stores the mail alias file), or simply run
       "newaliases" to build the necessary DBM or DB file.

       The local(8) delivery agent disallows regular expression substitution
       of $1 etc. in alias_maps, because that would open a security hole.

       The local(8) delivery agent will silently ignore requests to use the
       proxymap(8) server within alias_maps. Instead it will open the table
       directly. Before Postfix version 2.2, the local(8) delivery agent will
       terminate with a fatal error.

       Examples:

       alias_maps = hash:/etc/aliases, nis:mail.aliases
       alias_maps = hash:/etc/aliases

allow_mail_to_commands (default: alias, forward)
       Restrict local(8) mail delivery to external commands.  The default is
       to disallow delivery to "|command" in :include:  files (see aliases(5)
       for the text that defines this terminology).

       Specify zero or more of: alias, forward or include, in order to allow
       commands in aliases(5), .forward files or in :include:  files,
       respectively.

       Example:

       allow_mail_to_commands = alias,forward,include

allow_mail_to_files (default: alias, forward)
       Restrict local(8) mail delivery to external files. The default is to
       disallow "/file/name" destinations in :include:  files (see aliases(5)
       for the text that defines this terminology).

       Specify zero or more of: alias, forward or include, in order to allow
       "/file/name" destinations in aliases(5), .forward files and in
       :include:  files, respectively.

       Example:

       allow_mail_to_files = alias,forward,include

allow_min_user (default: no)
       Allow a sender or recipient address to have `-' as the first character.
       By default, this is not allowed, to avoid accidents with software that
       passes email addresses via the command line. Such software would not be
       able to distinguish a malicious address from a bona fide command-line
       option. Although this can be prevented by inserting a "--" option
       terminator into the command line, this is difficult to enforce
       consistently and globally.

       As of Postfix version 2.5, this feature is implemented by trivial-
       rewrite(8).  With earlier versions this feature was implemented by
       qmgr(8) and was limited to recipient addresses only.

allow_percent_hack (default: yes)
       Enable the rewriting of the form "user%domain" to "user@domain".  This
       is enabled by default.

       Note: with Postfix version 2.2, message header address rewriting
       happens only when one of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received from a network client that matches
              $local_header_rewrite_clients,

       o      The message is received from the network, and the
              remote_header_rewrite_domain parameter specifies a non-empty
              value.

       To get the behavior before Postfix version 2.2, specify
       "local_header_rewrite_clients = static:all".

       Example:

       allow_percent_hack = no

allow_untrusted_routing (default: no)
       Forward mail with sender-specified routing (user[@%!]remote[@%!]site)
       from untrusted clients to destinations matching $relay_domains.

       By default, this feature is turned off.  This closes a nasty open relay
       loophole where a backup MX host can be tricked into forwarding junk
       mail to a primary MX host which then spams it out to the world.

       This parameter also controls if non-local addresses with sender-
       specified routing can match Postfix access tables. By default, such
       addresses cannot match Postfix access tables, because the address is
       ambiguous.

alternate_config_directories (default: empty)
       A list of non-default Postfix configuration directories that may be
       specified with "-c config_directory" on the command line, or via the
       MAIL_CONFIG environment parameter.

       This list must be specified in the default Postfix configuration
       directory, and is used by set-gid Postfix commands such as postqueue(1)
       and postdrop(1).

always_add_missing_headers (default: no)
       Always add (Resent-) From:, To:, Date: or Message-ID: headers when not
       present.  Postfix 2.6 and later add these headers only when clients
       match the local_header_rewrite_clients parameter setting.  Earlier
       Postfix versions always add these headers; this may break DKIM
       signatures that cover non-existent headers.

always_bcc (default: empty)
       Optional address that receives a "blind carbon copy" of each message
       that is received by the Postfix mail system.

       Note: if mail to the BCC address bounces it will be returned to the
       sender.

       Note: automatic BCC recipients are produced only for new mail.  To
       avoid mailer loops, automatic BCC recipients are not generated after
       Postfix forwards mail internally, or after Postfix generates mail
       itself.

anvil_rate_time_unit (default: 60s)
       The time unit over which client connection rates and other rates are
       calculated.

       This feature is implemented by the anvil(8) service which is available
       in Postfix version 2.2 and later.

       The default interval is relatively short. Because of the high frequency
       of updates, the anvil(8) server uses volatile memory only. Thus,
       information is lost whenever the process terminates.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

anvil_status_update_time (default: 600s)
       How frequently the anvil(8) connection and rate limiting server logs
       peak usage information.

       This feature is available in Postfix 2.2 and later.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

append_at_myorigin (default: yes)
       With locally submitted mail, append the string "@$myorigin" to mail
       addresses without domain information. With remotely submitted mail,
       append the string "@$remote_header_rewrite_domain" instead.

       Note 1: this feature is enabled by default and must not be turned off.
       Postfix does not support domain-less addresses.

       Note 2: with Postfix version 2.2, message header address rewriting
       happens only when one of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received from a network client that matches
              $local_header_rewrite_clients,

       o      The message is received from the network, and the
              remote_header_rewrite_domain parameter specifies a non-empty
              value.

       To get the behavior before Postfix version 2.2, specify
       "local_header_rewrite_clients = static:all".

append_dot_mydomain (default: yes)
       With locally submitted mail, append the string ".$mydomain" to
       addresses that have no ".domain" information. With remotely submitted
       mail, append the string ".$remote_header_rewrite_domain" instead.

       Note 1: this feature is enabled by default. If disabled, users will not
       be able to send mail to "user@partialdomainname" but will have to
       specify full domain names instead.

       Note 2: with Postfix version 2.2, message header address rewriting
       happens only when one of the following conditions is true:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received from a network client that matches
              $local_header_rewrite_clients,

       o      The message is received from the network, and the
              remote_header_rewrite_domain parameter specifies a non-empty
              value.

       To get the behavior before Postfix version 2.2, specify
       "local_header_rewrite_clients = static:all".

application_event_drain_time (default: 100s)
       How long the postkick(1) command waits for a request to enter the
       server's input buffer before giving up.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

authorized_flush_users (default: static:anyone)
       List of users who are authorized to flush the queue.

       By default, all users are allowed to flush the queue.  Access is always
       granted if the invoking user is the super-user or the $mail_owner user.
       Otherwise, the real UID of the process is looked up in the system
       password file, and access is granted only if the corresponding login
       name is on the access list.  The username "unknown" is used for
       processes whose real UID is not found in the password file.

       Specify a list of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The list is matched left to
       right, and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude a name from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_mailq_users (default: static:anyone)
       List of users who are authorized to view the queue.

       By default, all users are allowed to view the queue.  Access is always
       granted if the invoking user is the super-user or the $mail_owner user.
       Otherwise, the real UID of the process is looked up in the system
       password file, and access is granted only if the corresponding login
       name is on the access list.  The username "unknown" is used for
       processes whose real UID is not found in the password file.

       Specify a list of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The list is matched left to
       right, and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude a user name from the list. The form "!/file/name"
       is supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_submit_users (default: static:anyone)
       List of users who are authorized to submit mail with the sendmail(1)
       command (and with the privileged postdrop(1) helper command).

       By default, all users are allowed to submit mail.  Otherwise, the real
       UID of the process is looked up in the system password file, and access
       is granted only if the corresponding login name is on the access list.
       The username "unknown" is used for processes whose real UID is not
       found in the password file. To deny mail submission access to all users
       specify an empty list.

       Specify a list of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The list is matched left to
       right, and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude a user name from the list. The form "!/file/name"
       is supported only in Postfix version 2.4 and later.

       Example:

       authorized_submit_users = !www, static:all

       This feature is available in Postfix 2.2 and later.

authorized_verp_clients (default: $mynetworks)
       What SMTP clients are allowed to specify the XVERP command.  This
       command requests that mail be delivered one recipient at a time with a
       per recipient return address.

       By default, only trusted clients are allowed to specify XVERP.

       This parameter was introduced with Postfix version 1.1.  Postfix
       version 2.1 renamed this parameter to smtpd_authorized_verp_clients and
       changed the default to none.

       Specify a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the network part
       of a host address. You can also specify hostnames or .domain names (the
       initial dot causes the domain to match any name below it),
       "/file/name" or "type:table" patterns.  A "/file/name" pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table entry matches a lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside [] in
       the authorized_verp_clients value, and in files specified with
       "/file/name".  IP version 6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

backwards_bounce_logfile_compatibility (default: yes)
       Produce additional bounce(8) logfile records that can be read by
       Postfix versions before 2.0. The current and more extensible "name =
       value" format is needed in order to implement more sophisticated
       functionality.

       This feature is available in Postfix 2.1 and later.

berkeley_db_create_buffer_size (default: 16777216)
       The per-table I/O buffer size for programs that create Berkeley DB hash
       or btree tables.  Specify a byte count.

       This feature is available in Postfix 2.0 and later.

berkeley_db_read_buffer_size (default: 131072)
       The per-table I/O buffer size for programs that read Berkeley DB hash
       or btree tables.  Specify a byte count.

       This feature is available in Postfix 2.0 and later.

best_mx_transport (default: empty)
       Where the Postfix SMTP client should deliver mail when it detects a
       "mail loops back to myself" error condition. This happens when the
       local MTA is the best SMTP mail exchanger for a destination not listed
       in $mydestination, $inet_interfaces, $proxy_interfaces,
       $virtual_alias_domains, or $virtual_mailbox_domains.  By default, the
       Postfix SMTP client returns such mail as undeliverable.

       Specify, for example, "best_mx_transport = local" to pass the mail from
       the Postfix SMTP client to the local(8) delivery agent. You can specify
       any message delivery "transport" or "transport:nexthop" that is defined
       in the master.cf file. See the transport(5) manual page for the syntax
       and meaning of "transport" or "transport:nexthop".

       However, this feature is expensive because it ties up a Postfix SMTP
       client process while the local(8) delivery agent is doing its work. It
       is more efficient (for Postfix) to list all hosted domains in a table
       or database.

biff (default: yes)
       Whether or not to use the local biff service.  This service sends "new
       mail" notifications to users who have requested new mail notification
       with the UNIX command "biff y".

       For compatibility reasons this feature is on by default.  On systems
       with lots of interactive users, the biff service can be a performance
       drain.  Specify "biff = no" in main.cf to disable.

body_checks (default: empty)
       Optional lookup tables for content inspection as specified in the
       body_checks(5) manual page.

       Note: with Postfix versions before 2.0, these rules inspect all content
       after the primary message headers.

body_checks_size_limit (default: 51200)
       How much text in a message body segment (or attachment, if you prefer
       to use that term) is subjected to body_checks inspection.  The amount
       of text is limited to avoid scanning huge attachments.

       This feature is available in Postfix 2.0 and later.

bounce_notice_recipient (default: postmaster)
       The recipient of postmaster notifications with the message headers of
       mail that Postfix did not deliver and of SMTP conversation transcripts
       of mail that Postfix did not receive.  This feature is enabled with the
       notify_classes parameter.

bounce_queue_lifetime (default: 5d)
       The maximal time a bounce message is queued before it is considered
       undeliverable.  By default, this is the same as the queue life time for
       regular mail.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is d (days).

       Specify 0 when mail delivery should be tried only once.

       This feature is available in Postfix 2.1 and later.

bounce_service_name (default: bounce)
       The name of the bounce(8) service. This service maintains a record of
       failed delivery attempts and generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

bounce_size_limit (default: 50000)
       The maximal amount of original message text that is sent in a non-
       delivery notification. Specify a byte count.  A message is returned as
       either message/rfc822 (the complete original) or as text/rfc822-headers
       (the headers only).  With Postfix version 2.4 and earlier, a message is
       always returned as message/rfc822 and is truncated when it exceeds the
       size limit.

       Notes:

       o      If you increase this limit, then you should increase the
              mime_nesting_limit value proportionally.

       o      Be careful when making changes.  Excessively large values will
              result in the loss of non-delivery notifications, when a bounce
              message size exceeds a local or remote MTA's message size limit.

bounce_template_file (default: empty)
       Pathname of a configuration file with bounce message templates.  These
       override the built-in templates of delivery status notification (DSN)
       messages for undeliverable mail, for delayed mail, successful delivery,
       or delivery verification. The bounce(5) manual page describes how to
       edit and test template files.

       Template message body text may contain $name references to Postfix
       configuration parameters. The result of $name expansion can be
       previewed with "postconf -b file_name" before the file is placed into
       the Postfix configuration directory.

       This feature is available in Postfix 2.3 and later.

broken_sasl_auth_clients (default: no)
       Enable inter-operability with SMTP clients that implement an obsolete
       version of the AUTH command (RFC 4954). Examples of such clients are
       MicroSoft Outlook Express version 4 and MicroSoft Exchange version 5.0.

       Specify "broken_sasl_auth_clients = yes" to have Postfix advertise AUTH
       support in a non-standard way.

canonical_classes (default: envelope_sender, envelope_recipient,
header_sender, header_recipient)
       What addresses are subject to canonical_maps address mapping.  By
       default, canonical_maps address mapping is applied to envelope sender
       and recipient addresses, and to header sender and header recipient
       addresses.

       Specify one or more of: envelope_sender, envelope_recipient,
       header_sender, header_recipient

       This feature is available in Postfix 2.2 and later.

canonical_maps (default: empty)
       Optional address mapping lookup tables for message headers and
       envelopes. The mapping is applied to both sender and recipient
       addresses, in both envelopes and in headers, as controlled with the
       canonical_classes parameter. This is typically used to clean up dirty
       addresses from legacy mail systems, or to replace login names by
       Firstname.Lastname.  The table format and lookups are documented in
       canonical(5). For an overview of Postfix address manipulations see the
       ADDRESS_REWRITING_README document.

       If you use this feature, run "postmap /etc/postfix/canonical" to build
       the necessary DBM or DB file after every change. The changes will
       become visible after a minute or so.  Use "postfix reload" to eliminate
       the delay.

       Note: with Postfix version 2.2, message header address mapping happens
       only when message header address rewriting is enabled:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received from a network client that matches
              $local_header_rewrite_clients,

       o      The message is received from the network, and the
              remote_header_rewrite_domain parameter specifies a non-empty
              value.

       To get the behavior before Postfix version 2.2, specify
       "local_header_rewrite_clients = static:all".

       Examples:

       canonical_maps = dbm:/etc/postfix/canonical
       canonical_maps = hash:/etc/postfix/canonical

cleanup_service_name (default: cleanup)
       The name of the cleanup(8) service. This service rewrites addresses
       into the standard form, and performs canonical(5) address mapping and
       virtual(5) aliasing.

       This feature is available in Postfix 2.0 and later.

command_directory (default: see postconf -d output)
       The location of all postfix administrative commands.

command_execution_directory (default: empty)
       The local(8) delivery agent working directory for delivery to external
       command.  Failure to change directory causes the delivery to be
       deferred.

       The following $name expansions are done on command_execution_directory
       before the directory is changed. Expansion happens in the context of
       the delivery request.  The result of $name expansion is filtered with
       the character set that is specified with the
       execution_directory_expansion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
              The full recipient address.

       $extension
              The optional recipient address extension.

       $domain
              The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
              The system-wide recipient address extension delimiter.

       ${name?value}
              Expands to value when $name is non-empty.

       ${name:value}
              Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       This feature is available in Postfix 2.2 and later.

command_expansion_filter (default: see postconf -d output)
       Restrict the characters that the local(8) delivery agent allows in
       $name expansions of $mailbox_command and $command_execution_directory.
       Characters outside the allowed set are replaced by underscores.

command_time_limit (default: 1000s)
       Time limit for delivery to external commands. This limit is used by the
       local(8) delivery agent, and is the default time limit for delivery by
       the pipe(8) delivery agent.

       Note: if you set this time limit to a large value you must update the
       global ipc_timeout parameter as well.

config_directory (default: see postconf -d output)
       The default location of the Postfix main.cf and master.cf configuration
       files. This can be overruled via the following mechanisms:

       o      The MAIL_CONFIG environment variable (daemon processes and
              commands).

       o      The "-c" command-line option (commands only).

       With Postfix command that run with set-gid privileges, a
       config_directory override requires either root privileges, or it
       requires that the directory is listed with the
       alternate_config_directories parameter in the default main.cf file.

connection_cache_protocol_timeout (default: 5s)
       Time limit for connection cache connect, send or receive operations.
       The time limit is enforced in the client.

       This feature is available in Postfix 2.3 and later.

connection_cache_service_name (default: scache)
       The name of the scache(8) connection cache service.  This service
       maintains a limited pool of cached sessions.

       This feature is available in Postfix 2.2 and later.

connection_cache_status_update_time (default: 600s)
       How frequently the scache(8) server logs usage statistics with
       connection cache hit and miss rates for logical destinations and for
       physical endpoints.

connection_cache_ttl_limit (default: 2s)
       The maximal time-to-live value that the scache(8) connection cache
       server allows. Requests that specify a larger TTL will be stored with
       the maximum allowed TTL. The purpose of this additional control is to
       protect the infrastructure against careless people. The cache TTL is
       already bounded by $max_idle.

content_filter (default: empty)
       After the message is queued, send the entire message to the specified
       transport:destination. The transport name specifies the first field of
       a mail delivery agent definition in master.cf; the syntax of the next-
       hop destination is described in the manual page of the corresponding
       delivery agent.  More information about external content filters is in
       the Postfix FILTER_README file.

       Notes:

       o      This setting has lower precedence than a FILTER action that is
              specified in an access(5), header_checks(5) or body_checks(5)
              table.

       o      The meaning of an empty next-hop filter destination is version
              dependent.  Postfix 2.7 and later will use the recipient domain;
              earlier versions will use $myhostname.  Specify
              "default_filter_nexthop = $myhostname" for compatibility with
              Postfix 2.6 or earlier, or specify a content_filter value with
              an explicit next-hop destination.

cyrus_sasl_config_path (default: empty)
       Search path for Cyrus SASL application configuration files, currently
       used only to locate the $smtpd_sasl_path.conf file.  Specify zero or
       more directories separated by a colon character, or an empty value to
       use Cyrus SASL's built-in search path.

       This feature is available in Postfix 2.5 and later when compiled with
       Cyrus SASL 2.1.22 or later.

daemon_directory (default: see postconf -d output)
       The directory with Postfix support programs and daemon programs.  These
       should not be invoked directly by humans. The directory must be owned
       by root.

daemon_timeout (default: 18000s)
       How much time a Postfix daemon process may take to handle a request
       before it is terminated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

data_directory (default: see postconf -d output)
       The directory with Postfix-writable data files (for example: caches,
       pseudo-random numbers).  This directory must be owned by the mail_owner
       account, and must not be shared with non-Postfix software.

       This feature is available in Postfix 2.5 and later.

debug_peer_level (default: 2)
       The increment in verbose logging level when a remote client or server
       matches a pattern in the debug_peer_list parameter.

debug_peer_list (default: empty)
       Optional list of remote client or server hostname or network address
       patterns that cause the verbose logging level to increase by the amount
       specified in $debug_peer_level.

       Specify domain names, network/netmask patterns, "/file/name" patterns
       or "type:table" lookup tables. The right-hand side result from
       "type:table" lookups is ignored.

       Pattern matching of domain names is controlled by the
       parent_domain_matches_subdomains parameter.

       Examples:

       debug_peer_list = 127.0.0.1
       debug_peer_list = example.com

debugger_command (default: empty)
       The external command to execute when a Postfix daemon program is
       invoked with the -D option.

       Use "command .. & sleep 5" so that the debugger can attach before the
       process marches on. If you use an X-based debugger, be sure to set up
       your XAUTHORITY environment variable before starting Postfix.

       Example:

       debugger_command =
           PATH=/usr/bin:/usr/X11R6/bin
           ddd $daemon_directory/$process_name $process_id & sleep 5

default_database_type (default: see postconf -d output)
       The default database type for use in newaliases(1), postalias(1) and
       postmap(1) commands. On many UNIX systems the default type is either
       dbm or hash. The default setting is frozen when the Postfix system is
       built.

       Examples:

       default_database_type = hash
       default_database_type = dbm

default_delivery_slot_cost (default: 5)
       How often the Postfix queue manager's scheduler is allowed to preempt
       delivery of one message with another.

       Each transport maintains a so-called "available delivery slot counter"
       for each message. One message can be preempted by another one when the
       other message can be delivered using no more delivery slots (i.e.,
       invocations of delivery agents) than the current message counter has
       accumulated (or will eventually accumulate - see about slot loans
       below). This parameter controls how often is the counter incremented -
       it happens after each default_delivery_slot_cost recipients have been
       delivered.

       The cost of 0 is used to disable the preempting scheduling completely.
       The minimum value the scheduling algorithm can use is 2 - use it if you
       want to maximize the message throughput rate. Although there is no
       maximum, it doesn't make much sense to use values above say 50.

       The only reason why the value of 2 is not the default is the way this
       parameter affects the delivery of mailing-list mail. In the worst case,
       their delivery can take somewhere between (cost+1/cost) and
       (cost/cost-1) times more than if the preemptive scheduler was disabled.
       The default value of 5 turns out to provide reasonable message response
       times while making sure the mailing-list deliveries are not extended by
       more than 20-25 percent even in the worst case.

       Use transport_delivery_slot_cost to specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       Examples:

       default_delivery_slot_cost = 0
       default_delivery_slot_cost = 2

default_delivery_slot_discount (default: 50)
       The default value for transport-specific _delivery_slot_discount
       settings.

       This parameter speeds up the moment when a message preemption can
       happen. Instead of waiting until the full amount of delivery slots
       required is available, the preemption can happen when
       transport_delivery_slot_discount percent of the required amount plus
       transport_delivery_slot_loan still remains to be accumulated.  Note
       that the full amount will still have to be accumulated before another
       preemption can take place later.

       Use transport_delivery_slot_discount to specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_delivery_slot_loan (default: 3)
       The default value for transport-specific _delivery_slot_loan settings.

       This parameter speeds up the moment when a message preemption can
       happen. Instead of waiting until the full amount of delivery slots
       required is available, the preemption can happen when
       transport_delivery_slot_discount percent of the required amount plus
       transport_delivery_slot_loan still remains to be accumulated.  Note
       that the full amount will still have to be accumulated before another
       preemption can take place later.

       Use transport_delivery_slot_loan to specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_destination_concurrency_failed_cohort_limit (default: 1)
       How many pseudo-cohorts must suffer connection or handshake failure
       before a specific destination is considered unavailable (and further
       delivery is suspended). Specify zero to disable this feature. A
       destination's pseudo-cohort failure count is reset each time a delivery
       completes without connection or handshake failure for that specific
       destination.

       A pseudo-cohort is the number of deliveries equal to a destination's
       delivery concurrency.

       Use transport_destination_concurrency_failed_cohort_limit to specify a
       transport-specific override, where transport is the master.cf name of
       the message delivery transport.

       This feature is available in Postfix 2.5. The default setting is
       compatible with earlier Postfix versions.

default_destination_concurrency_limit (default: 20)
       The default maximal number of parallel deliveries to the same
       destination.  This is the default limit for delivery via the lmtp(8),
       pipe(8), smtp(8) and virtual(8) delivery agents.  With per-destination
       recipient limit > 1, a destination is a domain, otherwise it is a
       recipient.

       Use transport_destination_concurrency_limit to specify a transport-
       specific override, where transport is the master.cf name of the message
       delivery transport.

default_destination_concurrency_negative_feedback (default: 1)
       The per-destination amount of delivery concurrency negative feedback,
       after a delivery completes with a connection or handshake failure.
       Feedback values are in the range 0..1 inclusive. With negative
       feedback, concurrency is decremented at the beginning of a sequence of
       length 1/feedback. This is unlike positive feedback, where concurrency
       is incremented at the end of a sequence of length 1/feedback.

       As of Postfix version 2.5, negative feedback cannot reduce delivery
       concurrency to zero.  Instead, a destination is marked dead (further
       delivery suspended) after the failed pseudo-cohort count reaches
       $default_destination_concurrency_failed_cohort_limit (or
       $transport_destination_concurrency_failed_cohort_limit).  To make the
       scheduler completely immune to connection or handshake failures,
       specify a zero feedback value and a zero failed pseudo-cohort limit.

       Specify one of the following forms:

       number

       number / number
              Constant feedback. The value must be in the range 0..1
              inclusive.  The default setting of "1" is compatible with
              Postfix versions before 2.5, where a destination's delivery
              concurrency is throttled down to zero (and further delivery
              suspended) after a single failed pseudo-cohort.

       number / concurrency
              Variable feedback of "number / (delivery concurrency)".  The
              number must be in the range 0..1 inclusive. With number equal to
              "1", a destination's delivery concurrency is decremented by 1
              after each failed pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal to a destination's
       delivery concurrency.

       Use transport_destination_concurrency_negative_feedback to specify a
       transport-specific override, where transport is the master.cf name of
       the message delivery transport.

       This feature is available in Postfix 2.5. The default setting is
       compatible with earlier Postfix versions.

default_destination_concurrency_positive_feedback (default: 1)
       The per-destination amount of delivery concurrency positive feedback,
       after a delivery completes without connection or handshake failure.
       Feedback values are in the range 0..1 inclusive.  The concurrency
       increases until it reaches the per-destination maximal concurrency
       limit. With positive feedback, concurrency is incremented at the end of
       a sequence with length 1/feedback. This is unlike negative feedback,
       where concurrency is decremented at the start of a sequence of length
       1/feedback.

       Specify one of the following forms:

       number

       number / number
              Constant feedback.  The value must be in the range 0..1
              inclusive. The default setting of "1" is compatible with Postfix
              versions before 2.5, where a destination's delivery concurrency
              doubles after each successful pseudo-cohort.

       number / concurrency
              Variable feedback of "number / (delivery concurrency)".  The
              number must be in the range 0..1 inclusive. With number equal to
              "1", a destination's delivery concurrency is incremented by 1
              after each successful pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal to a destination's
       delivery concurrency.

       Use transport_destination_concurrency_positive_feedback to specify a
       transport-specific override, where transport is the master.cf name of
       the message delivery transport.

       This feature is available in Postfix 2.5 and later.

default_destination_rate_delay (default: 0s)
       The default amount of delay that is inserted between individual
       deliveries to the same destination; with per-destination recipient
       limit > 1, a destination is a domain, otherwise it is a recipient.

       To enable the delay, specify a non-zero time value (an integral value
       plus an optional one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       NOTE: the delay is enforced by the queue manager. The delay timer state
       does not survive "postfix reload" or "postfix stop".

       Use transport_destination_rate_delay to specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       NOTE: with a non-zero _destination_rate_delay, specify a
       transport_destination_concurrency_failed_cohort_limit of 10 or more to
       prevent Postfix from deferring all mail for the same destination after
       only one connection or handshake error.

       This feature is available in Postfix 2.5 and later.

default_destination_recipient_limit (default: 50)
       The default maximal number of recipients per message delivery.  This is
       the default limit for delivery via the lmtp(8), pipe(8), smtp(8) and
       virtual(8) delivery agents.

       Setting this parameter to a value of 1 changes the meaning of the
       corresponding per-destination concurrency limit from concurrency per
       domain into concurrency per recipient.

       Use transport_destination_recipient_limit to specify a transport-
       specific override, where transport is the master.cf name of the message
       delivery transport.

default_extra_recipient_limit (default: 1000)
       The default value for the extra per-transport limit imposed on the
       number of in-memory recipients.  This extra recipient space is reserved
       for the cases when the Postfix queue manager's scheduler preempts one
       message with another and suddenly needs some extra recipients slots for
       the chosen message in order to avoid performance degradation.

       Use transport_extra_recipient_limit to specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_filter_nexthop (default: empty)
       When a content_filter or FILTER request specifies no explicit next-hop
       destination, use $default_filter_nexthop instead; when that value is
       empty, use the domain in the recipient address.  Specify
       "default_filter_nexthop = $myhostname" for compatibility with Postfix
       version 2.6 and earlier, or specify an explicit next-hop destination
       with each content_filter value or FILTER action.

       This feature is available in Postfix 2.7 and later.

default_minimum_delivery_slots (default: 3)
       How many recipients a message must have in order to invoke the Postfix
       queue manager's scheduling algorithm at all.  Messages which would
       never accumulate at least this many delivery slots (subject to slot
       cost parameter as well) are never preempted.

       Use transport_minimum_delivery_slots to specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_privs (default: nobody)
       The default rights used by the local(8) delivery agent for delivery to
       external file or command.  These rights are used when delivery is
       requested from an aliases(5) file that is owned by root, or when
       delivery is done on behalf of root. DO NOT SPECIFY A PRIVILEGED USER OR
       THE POSTFIX OWNER.

default_process_limit (default: 100)
       The default maximal number of Postfix child processes that provide a
       given service. This limit can be overruled for specific services in the
       master.cf file.

default_rbl_reply (default: see postconf -d output)
       The default SMTP server response template for a request that is
       rejected by an RBL-based restriction. This template can be overruled by
       specific entries in the optional rbl_reply_maps lookup table.

       This feature is available in Postfix 2.0 and later.

       The template is subject to exactly one level of $name substitution:

       $client
              The client hostname and IP address, formatted as name[address].

       $client_address
              The client IP address.

       $client_name
              The client hostname or "unknown". See
              reject_unknown_client_hostname for more details.

       $reverse_client_name
              The client hostname from address->name lookup, or "unknown".
              See reject_unknown_reverse_client_hostname for more details.

       $helo_name
              The hostname given in HELO or EHLO command or empty string.

       $rbl_class
              The blacklisted entity type: Client host, Helo command, Sender
              address, or Recipient address.

       $rbl_code
              The numerical SMTP response code, as specified with the
              maps_rbl_reject_code configuration parameter. Note: The
              numerical SMTP response code is required, and must appear at the
              start of the reply. With Postfix version 2.3 and later this
              information may be followed by an RFC 3463 enhanced status code.

       $rbl_domain
              The RBL domain where $rbl_what is blacklisted.

       $rbl_reason
              The reason why $rbl_what is blacklisted, or an empty string.

       $rbl_what
              The entity that is blacklisted (an IP address, a hostname, a
              domain name, or an email address whose domain was blacklisted).

       $recipient
              The recipient address or <> in case of the null address.

       $recipient_domain
              The recipient domain or empty string.

       $recipient_name
              The recipient address localpart or <> in case of null address.

       $sender
              The sender address or <> in case of the null address.

       $sender_domain
              The sender domain or empty string.

       $sender_name
              The sender address localpart or <> in case of the null address.

       ${name?text}
              Expands to `text' if $name is not empty.

       ${name:text}
              Expands to `text' if $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Note: when an enhanced status code is specified in an RBL reply
       template, it is subject to modification.  The following transformations
       are needed when the same RBL reply template is used for client, helo,
       sender, or recipient access restrictions.

       o      When rejecting a sender address, the Postfix SMTP server will
              transform a recipient DSN status (e.g., 4.1.1-4.1.6) into the
              corresponding sender DSN status, and vice versa.

       o      When rejecting non-address information (such as the HELO command
              argument or the client hostname/address), the Postfix SMTP
              server will transform a sender or recipient DSN status into a
              generic non-address DSN status (e.g., 4.0.0).

default_recipient_limit (default: 20000)
       The default per-transport upper limit on the number of in-memory
       recipients.  These limits take priority over the global
       qmgr_message_recipient_limit after the message has been assigned to the
       respective transports.  See also default_extra_recipient_limit and
       qmgr_message_recipient_minimum.

       Use transport_recipient_limit to specify a transport-specific override,
       where transport is the master.cf name of the message delivery
       transport.

default_recipient_refill_delay (default: 5s)
       The default per-transport maximum delay between recipients refills.
       When not all message recipients fit into the memory at once, keep
       loading more of them at least once every this many seconds.  This is
       used to make sure the recipients are refilled in timely manner even
       when $default_recipient_refill_limit is too high for too slow
       deliveries.

       Use transport_recipient_refill_delay to specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       This feature is available in Postfix 2.4 and later.

default_recipient_refill_limit (default: 100)
       The default per-transport limit on the number of recipients refilled at
       once.  When not all message recipients fit into the memory at once,
       keep loading more of them in batches of at least this many at a time.
       See also $default_recipient_refill_delay, which may result in recipient
       batches lower than this when this limit is too high for too slow
       deliveries.

       Use transport_recipient_refill_limit to specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       This feature is available in Postfix 2.4 and later.

default_transport (default: smtp)
       The default mail delivery transport and next-hop destination for
       destinations that do not match $mydestination, $inet_interfaces,
       $proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains, or
       $relay_domains.  This information can be overruled with the
       sender_dependent_default_transport_maps parameter and with the
       transport(5) table.

       In order of decreasing precedence, the nexthop destination is taken
       from $sender_dependent_default_transport_maps, $default_transport,
       $sender_dependent_relayhost_maps, $relayhost, or from the recipient
       domain.

       Specify a string of the form transport:nexthop, where transport is the
       name of a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       Example:

       default_transport = uucp:relayhostname

default_verp_delimiters (default: +=)
       The two default VERP delimiter characters. These are used when no
       explicit delimiters are specified with the SMTP XVERP command or with
       the "sendmail -V" command-line option. Specify characters that are
       allowed by the verp_delimiter_filter setting.

       This feature is available in Postfix 1.1 and later.

defer_code (default: 450)
       The numerical Postfix SMTP server response code when a remote SMTP
       client request is rejected by the "defer" restriction.

       Do not change this unless you have a complete understanding of RFC
       2821.

defer_service_name (default: defer)
       The name of the defer service. This service is implemented by the
       bounce(8) daemon and maintains a record of failed delivery attempts and
       generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

defer_transports (default: empty)
       The names of message delivery transports that should not deliver mail
       unless someone issues "sendmail -q" or equivalent. Specify zero or more
       names of mail delivery transports names that appear in the first field
       of master.cf.

       Example:

       defer_transports = smtp

delay_logging_resolution_limit (default: 2)
       The maximal number of digits after the decimal point when logging sub-
       second delay values.  Specify a number in the range 0..6.

       Large delay values are rounded off to an integral number seconds; delay
       values below the delay_logging_resolution_limit are logged as "0", and
       small delay values are logged with at most two-digit precision.

       The format of the "delays=a/b/c/d" logging is as follows:

       o      a = time from message arrival to last active queue entry

       o      b = time from last active queue entry to connection setup

       o      c = time in connection setup, including DNS, EHLO and STARTTLS

       o      d = time in message transmission

       This feature is available in Postfix 2.3 and later.

delay_notice_recipient (default: postmaster)
       The recipient of postmaster notifications with the message headers of
       mail that cannot be delivered within $delay_warning_time time units.

       This feature is enabled with the delay_warning_time parameter.

delay_warning_time (default: 0h)
       The time after which the sender receives the message headers of mail
       that is still queued.

       To enable this feature, specify a non-zero time value (an integral
       value plus an optional one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is h (hours).

deliver_lock_attempts (default: 20)
       The maximal number of attempts to acquire an exclusive lock on a
       mailbox file or bounce(8) logfile.

deliver_lock_delay (default: 1s)
       The time between attempts to acquire an exclusive lock on a mailbox
       file or bounce(8) logfile.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

destination_concurrency_feedback_debug (default: no)
       Make the queue manager's feedback algorithm verbose for performance
       analysis purposes.

       This feature is available in Postfix 2.5 and later.

detect_8bit_encoding_header (default: yes)
       Automatically detect 8BITMIME body content by looking at Content-
       Transfer-Encoding: message headers; historically, this behavior was
       hard-coded to be "always on".

       This feature is available in Postfix 2.5 and later.

disable_dns_lookups (default: no)
       Disable DNS lookups in the Postfix SMTP and LMTP clients. When
       disabled, hosts are looked up with the getaddrinfo() system library
       routine which normally also looks in /etc/hosts.

       DNS lookups are enabled by default.

disable_mime_input_processing (default: no)
       Turn off MIME processing while receiving mail. This means that no
       special treatment is given to Content-Type: message headers, and that
       all text after the initial message headers is considered to be part of
       the message body.

       This feature is available in Postfix 2.0 and later.

       Mime input processing is enabled by default, and is needed in order to
       recognize MIME headers in message content.

disable_mime_output_conversion (default: no)
       Disable the conversion of 8BITMIME format to 7BIT format.  Mime output
       conversion is needed when the destination does not advertise 8BITMIME
       support.

       This feature is available in Postfix 2.0 and later.

disable_verp_bounces (default: no)
       Disable sending one bounce report per recipient.

       The default, one per recipient, is what ezmlm needs.

       This feature is available in Postfix 1.1 and later.

disable_vrfy_command (default: no)
       Disable the SMTP VRFY command. This stops some techniques used to
       harvest email addresses.

       Example:

       disable_vrfy_command = no

dnsblog_reply_delay (default: 0s)
       A debugging aid to artifically delay DNS responses.

       This feature is available in Postfix 2.8.

dnsblog_service_name (default: dnsblog)
       The name of the dnsblog(8) service entry in master.cf. This service
       performs DNS white/blacklist lookups.

       This feature is available in Postfix 2.8 and later.

dont_remove (default: 0)
       Don't remove queue files and save them to the "saved" mail queue.  This
       is a debugging aid.  To inspect the envelope information and content of
       a Postfix queue file, use the postcat(1) command.

double_bounce_sender (default: double-bounce)
       The sender address of postmaster notifications that are generated by
       the mail system. All mail to this address is silently discarded, in
       order to terminate mail bounce loops.

duplicate_filter_limit (default: 1000)
       The maximal number of addresses remembered by the address duplicate
       filter for aliases(5) or virtual(5) alias expansion, or for showq(8)
       queue displays.

empty_address_default_transport_maps_lookup_key (default: <&lt;>&gt;)
       The sender_dependent_default_transport_maps search string that will be
       used instead of the null sender address.

       This feature is available in Postfix 2.7 and later.

empty_address_recipient (default: MAILER-DAEMON)
       The recipient of mail addressed to the null address.  Postfix does not
       accept such addresses in SMTP commands, but they may still be created
       locally as the result of configuration or software error.

empty_address_relayhost_maps_lookup_key (default: <&lt;>&gt;)
       The sender_dependent_relayhost_maps search string that will be used
       instead of the null sender address.

       This feature is available in Postfix 2.5 and later. With earlier
       versions, sender_dependent_relayhost_maps lookups were skipped for the
       null sender address.

enable_errors_to (default: no)
       Report mail delivery errors to the address specified with the non-
       standard Errors-To: message header, instead of the envelope sender
       address (this feature is removed with Postfix version 2.2, is turned
       off by default with Postfix version 2.1, and is always turned on with
       older Postfix versions).

enable_original_recipient (default: yes)
       Enable support for the X-Original-To message header. This header is
       needed for multi-recipient mailboxes.

       When this parameter is set to yes, the cleanup(8) daemon performs
       duplicate elimination on distinct pairs of (original recipient,
       rewritten recipient), and generates non-empty original recipient queue
       file records.

       When this parameter is set to no, the cleanup(8) daemon performs
       duplicate elimination on the rewritten recipient address only, and
       generates empty original recipient queue file records.

       This feature is available in Postfix 2.1 and later. With Postfix
       version 2.0, support for the X-Original-To message header is always
       turned on. Postfix versions before 2.0 have no support for the X-
       Original-To message header.

error_notice_recipient (default: postmaster)
       The recipient of postmaster notifications about mail delivery problems
       that are caused by policy, resource, software or protocol errors.
       These notifications are enabled with the notify_classes parameter.

error_service_name (default: error)
       The name of the error(8) pseudo delivery agent. This service always
       returns mail as undeliverable.

       This feature is available in Postfix 2.0 and later.

execution_directory_expansion_filter (default: see postconf -d output)
       Restrict the characters that the local(8) delivery agent allows in
       $name expansions of $command_execution_directory.  Characters outside
       the allowed set are replaced by underscores.

       This feature is available in Postfix 2.2 and later.

expand_owner_alias (default: no)
       When delivering to an alias "aliasname" that has an "owner-aliasname"
       companion alias, set the envelope sender address to the expansion of
       the "owner-aliasname" alias. Normally, Postfix sets the envelope sender
       address to the name of the "owner-aliasname" alias.

export_environment (default: see postconf -d output)
       The list of environment variables that a Postfix process will export to
       non-Postfix processes. The TZ variable is needed for sane time keeping
       on System-V-ish systems.

       Specify a list of names and/or name=value pairs, separated by
       whitespace or comma. The name=value form is supported with Postfix
       version 2.1 and later.

       Example:

       export_environment = TZ PATH=/bin:/usr/bin

extract_recipient_limit (default: 10240)
       The maximal number of recipient addresses that Postfix will extract
       from message headers when mail is submitted with "sendmail -t".

       This feature was removed in Postfix version 2.1.

fallback_relay (default: empty)
       Optional list of relay hosts for SMTP destinations that can't be found
       or that are unreachable. With Postfix 2.3 this parameter is renamed to
       smtp_fallback_relay.

       By default, mail is returned to the sender when a destination is not
       found, and delivery is deferred when a destination is unreachable.

       The fallback relays must be SMTP destinations. Specify a domain, host,
       host:port, [host]:port, [address] or [address]:port; the form [host]
       turns off MX lookups.  If you specify multiple SMTP destinations,
       Postfix will try them in the specified order.

       Note: before Postfix 2.2, do not use the fallback_relay feature when
       relaying mail for a backup or primary MX domain. Mail would loop
       between the Postfix MX host and the fallback_relay host when the final
       destination is unavailable.

       o      In main.cf specify "relay_transport = relay",

       o      In master.cf specify "-o fallback_relay =" (i.e., empty) at the
              end of the relay entry.

       o      In transport maps, specify "relay:nexthop..." as the right-hand
              side for backup or primary MX domain entries.

       Postfix version 2.2 and later will not use the fallback_relay feature
       for destinations that it is MX host for.

fallback_transport (default: empty)
       Optional message delivery transport that the local(8) delivery agent
       should use for names that are not found in the aliases(5) or UNIX
       password database.

       The precedence of local(8) delivery features from high to low is:
       aliases, .forward files, mailbox_transport_maps, mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,
       mail_spool_directory, fallback_transport_maps, fallback_transport and
       luser_relay.

fallback_transport_maps (default: empty)
       Optional lookup tables with per-recipient message delivery transports
       for recipients that the local(8) delivery agent could not find in the
       aliases(5) or UNIX password database.

       The precedence of local(8) delivery features from high to low is:
       aliases, .forward files, mailbox_transport_maps, mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,
       mail_spool_directory, fallback_transport_maps, fallback_transport and
       luser_relay.

       For safety reasons, this feature does not allow $number substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

fast_flush_domains (default: $relay_domains)
       Optional list of destinations that are eligible for per-destination
       logfiles with mail that is queued to those destinations.

       By default, Postfix maintains "fast flush" logfiles only for
       destinations that the Postfix SMTP server is willing to relay to (i.e.
       the default is: "fast_flush_domains = $relay_domains"; see the
       relay_domains parameter in the postconf(5) manual).

       Specify a list of hosts or domains, "/file/name" patterns or
       "type:table" lookup tables, separated by commas and/or whitespace.
       Continue long lines by starting the next line with whitespace. A
       "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table is matched when the domain or its parent domain appears as lookup
       key.

       Specify "fast_flush_domains =" (i.e., empty) to disable the feature
       altogether.

fast_flush_purge_time (default: 7d)
       The time after which an empty per-destination "fast flush" logfile is
       deleted.

       You can specify the time as a number, or as a number followed by a
       letter that indicates the time unit: s=seconds, m=minutes, h=hours,
       d=days, w=weeks.  The default time unit is days.

fast_flush_refresh_time (default: 12h)
       The time after which a non-empty but unread per-destination "fast
       flush" logfile needs to be refreshed.  The contents of a logfile are
       refreshed by requesting delivery of all messages listed in the logfile.

       You can specify the time as a number, or as a number followed by a
       letter that indicates the time unit: s=seconds, m=minutes, h=hours,
       d=days, w=weeks.  The default time unit is hours.

fault_injection_code (default: 0)
       Force specific internal tests to fail, to test the handling of errors
       that are difficult to reproduce otherwise.

flush_service_name (default: flush)
       The name of the flush(8) service. This service maintains per-
       destination logfiles with the queue file names of mail that is queued
       for those destinations.

       This feature is available in Postfix 2.0 and later.

fork_attempts (default: 5)
       The maximal number of attempts to fork() a child process.

fork_delay (default: 1s)
       The delay between attempts to fork() a child process.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

forward_expansion_filter (default: see postconf -d output)
       Restrict the characters that the local(8) delivery agent allows in
       $name expansions of $forward_path.  Characters outside the allowed set
       are replaced by underscores.

forward_path (default: see postconf -d output)
       The local(8) delivery agent search list for finding a .forward file
       with user-specified delivery methods. The first file that is found is
       used.

       The following $name expansions are done on forward_path before the
       search actually happens. The result of $name expansion is filtered with
       the character set that is specified with the forward_expansion_filter
       parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
              The full recipient address.

       $extension
              The optional recipient address extension.

       $domain
              The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
              The system-wide recipient address extension delimiter.

       ${name?value}
              Expands to value when $name is non-empty.

       ${name:value}
              Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Examples:

       forward_path = /var/forward/$user
       forward_path =
           /var/forward/$user/.forward$recipient_delimiter$extension,
           /var/forward/$user/.forward

frozen_delivered_to (default: yes)
       Update the local(8) delivery agent's idea of the Delivered-To: address
       (see prepend_delivered_header) only once, at the start of a delivery
       attempt; do not update the Delivered-To: address while expanding
       aliases or .forward files.

       This feature is available in Postfix 2.3 and later. With older Postfix
       releases, the behavior is as if this parameter is set to "no". The old
       setting can be expensive with deeply nested aliases or .forward files.
       When an alias or .forward file changes the Delivered-To: address, it
       ties up one queue file and one cleanup process instance while mail is
       being forwarded.

hash_queue_depth (default: 1)
       The number of subdirectory levels for queue directories listed with the
       hash_queue_names parameter.

       After changing the hash_queue_names or hash_queue_depth parameter,
       execute the command "postfix reload".

hash_queue_names (default: deferred, defer)
       The names of queue directories that are split across multiple
       subdirectory levels.

       Before Postfix version 2.2, the default list of hashed queues was
       significantly larger. Claims about improvements in file system
       technology suggest that hashing of the incoming and active queues is no
       longer needed. Fewer hashed directories speed up the time needed to
       restart Postfix.

       After changing the hash_queue_names or hash_queue_depth parameter,
       execute the command "postfix reload".

header_address_token_limit (default: 10240)
       The maximal number of address tokens are allowed in an address message
       header. Information that exceeds the limit is discarded.  The limit is
       enforced by the cleanup(8) server.

header_checks (default: empty)
       Optional lookup tables for content inspection of primary non-MIME
       message headers, as specified in the header_checks(5) manual page.

header_size_limit (default: 102400)
       The maximal amount of memory in bytes for storing a message header.  If
       a header is larger, the excess is discarded.  The limit is enforced by
       the cleanup(8) server.

helpful_warnings (default: yes)
       Log warnings about problematic configuration settings, and provide
       helpful suggestions.

       This feature is available in Postfix 2.0 and later.

home_mailbox (default: empty)
       Optional pathname of a mailbox file relative to a local(8) user's home
       directory.

       Specify a pathname ending in "/" for qmail-style delivery.

       The precedence of local(8) delivery features from high to low is:
       aliases, .forward files, mailbox_transport_maps, mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,
       mail_spool_directory, fallback_transport_maps, fallback_transport and
       luser_relay.

       Examples:

       home_mailbox = Mailbox
       home_mailbox = Maildir/

hopcount_limit (default: 50)
       The maximal number of Received:  message headers that is allowed in the
       primary message headers. A message that exceeds the limit is bounced,
       in order to stop a mailer loop.

html_directory (default: see postconf -d output)
       The location of Postfix HTML files that describe how to build,
       configure or operate a specific Postfix subsystem or feature.

ignore_mx_lookup_error (default: no)
       Ignore DNS MX lookups that produce no response.  By default, the
       Postfix SMTP client defers delivery and tries again after some delay.
       This behavior is required by the SMTP standard.

       Specify "ignore_mx_lookup_error = yes" to force a DNS A record lookup
       instead. This violates the SMTP standard and can result in mis-delivery
       of mail.

import_environment (default: see postconf -d output)
       The list of environment parameters that a Postfix process will import
       from a non-Postfix parent process. Examples of relevant parameters:

       TZ     Needed for sane time keeping on most System-V-ish systems.

       DISPLAY
              Needed for debugging Postfix daemons with an X-windows debugger.

       XAUTHORITY
              Needed for debugging Postfix daemons with an X-windows debugger.

       MAIL_CONFIG
              Needed to make "postfix -c" work.

       Specify a list of names and/or name=value pairs, separated by
       whitespace or comma. The name=value form is supported with Postfix
       version 2.1 and later.

in_flow_delay (default: 1s)
       Time to pause before accepting a new message, when the message arrival
       rate exceeds the message delivery rate. This feature is turned on by
       default (it's disabled on SCO UNIX due to an SCO bug).

       With the default 100 SMTP server process limit, "in_flow_delay = 1s"
       limits the mail inflow to 100 messages per second above the number of
       messages delivered per second.

       Specify 0 to disable the feature. Valid delays are 0..10.

inet_interfaces (default: all)
       The network interface addresses that this mail system receives mail on.
       Specify "all" to receive mail on all network interfaces (default), and
       "loopback-only" to receive mail on loopback network interfaces only
       (Postfix version 2.2 and later).  The parameter also controls delivery
       of mail to user@[ip.address].

       Note 1: you need to stop and start Postfix when this parameter changes.

       Note 2: address information may be enclosed inside [], but this form is
       not required here.

       When inet_interfaces specifies just one IPv4 and/or IPv6 address that
       is not a loopback address, the Postfix SMTP client will use this
       address as the IP source address for outbound mail. Support for IPv6 is
       available in Postfix version 2.2 and later.

       On a multi-homed firewall with separate Postfix instances listening on
       the "inside" and "outside" interfaces, this can prevent each instance
       from being able to reach servers on the "other side" of the firewall.
       Setting smtp_bind_address to 0.0.0.0 avoids the potential problem for
       IPv4, and setting smtp_bind_address6 to :: solves the problem for IPv6.

       A better solution for multi-homed firewalls is to leave inet_interfaces
       at the default value and instead use explicit IP addresses in the
       master.cf SMTP server definitions.  This preserves the Postfix SMTP
       client's loop detection, by ensuring that each side of the firewall
       knows that the other IP address is still the same host. Setting
       $inet_interfaces to a single IPv4 and/or IPV6 address is primarily
       useful with virtual hosting of domains on secondary IP addresses, when
       each IP address serves a different domain (and has a different
       $myhostname setting).

       See also the proxy_interfaces parameter, for network addresses that are
       forwarded to Postfix by way of a proxy or address translator.

       Examples:

       inet_interfaces = all (DEFAULT)
       inet_interfaces = loopback-only (Postfix version 2.2 and later)
       inet_interfaces = 127.0.0.1
       inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
       inet_interfaces = 192.168.1.2, 127.0.0.1

inet_protocols (default: ipv4)
       The Internet protocols Postfix will attempt to use when making or
       accepting connections. Specify one or more of "ipv4" or "ipv6",
       separated by whitespace or commas. The form "all" is equivalent to
       "ipv4, ipv6" or "ipv4", depending on whether the operating system
       implements IPv6.

       This feature is available in Postfix 2.2 and later.

       Note: you MUST stop and start Postfix after changing this parameter.

       On systems that pre-date IPV6_V6ONLY support (RFC 3493), an IPv6 server
       will also accept IPv4 connections, even when IPv4 is turned off with
       the inet_protocols parameter.  On systems with IPV6_V6ONLY support,
       Postfix will use separate server sockets for IPv6 and IPv4, and each
       will accept only connections for the corresponding protocol.

       When IPv4 support is enabled via the inet_protocols parameter, Postfix
       will to DNS type A record lookups, and will convert IPv4-in-IPv6 client
       IP addresses (::ffff:1.2.3.4) to their original IPv4 form (1.2.3.4).
       The latter is needed on hosts that pre-date IPV6_V6ONLY support (RFC
       3493).

       When IPv6 support is enabled via the inet_protocols parameter, Postfix
       will do DNS type AAAA record lookups.

       When both IPv4 and IPv6 support are enabled, the Postfix SMTP client
       will attempt to connect via IPv6 before attempting to use IPv4.

       Examples:

       inet_protocols = ipv4 (DEFAULT)
       inet_protocols = all
       inet_protocols = ipv6
       inet_protocols = ipv4, ipv6

initial_destination_concurrency (default: 5)
       The initial per-destination concurrency level for parallel delivery to
       the same destination.  With per-destination recipient limit > 1, a
       destination is a domain, otherwise it is a recipient.

       Use transport_initial_destination_concurrency to specify a transport-
       specific override, where transport is the master.cf name of the message
       delivery transport (Postfix 2.5 and later).

       Warning: with concurrency of 1, one bad message can be enough to block
       all mail to a site.

internal_mail_filter_classes (default: empty)
       What categories of Postfix-generated mail are subject to before-queue
       content inspection by non_smtpd_milters, header_checks and body_checks.
       Specify zero or more of the following, separated by whitespace or
       comma.

       bounce Inspect the content of delivery status notifications.

       notify Inspect the content of postmaster notifications by the smtp(8)
              and smtpd(8) processes.

       NOTE: It's generally not safe to enable content inspection of Postfix-
       generated email messages. The user is warned.

       This feature is available in Postfix 2.3 and later.

invalid_hostname_reject_code (default: 501)
       The numerical Postfix SMTP server response code when the client HELO or
       EHLO command parameter is rejected by the reject_invalid_helo_hostname
       restriction.

       Do not change this unless you have a complete understanding of RFC
       2821.

ipc_idle (default: version dependent)
       The time after which a client closes an idle internal communication
       channel.  The purpose is to allow servers to terminate voluntarily
       after they become idle. This is used, for example, by the address
       resolving and rewriting clients.

       With Postfix 2.4 the default value was reduced from 100s to 5s.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

ipc_timeout (default: 3600s)
       The time limit for sending or receiving information over an internal
       communication channel.  The purpose is to break out of deadlock
       situations. If the time limit is exceeded the software aborts with a
       fatal error.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

ipc_ttl (default: 1000s)
       The time after which a client closes an active internal communication
       channel.  The purpose is to allow servers to terminate voluntarily
       after reaching their client limit.  This is used, for example, by the
       address resolving and rewriting clients.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

line_length_limit (default: 2048)
       Upon input, long lines are chopped up into pieces of at most this
       length; upon delivery, long lines are reconstructed.

lmtp_address_preference (default: ipv6)
       The LMTP-specific version of the smtp_address_preference configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_assume_final (default: no)
       When an LMTP server announces no DSN support, assume that the server
       performs final delivery, and send "delivered" delivery status
       notifications instead of "relayed". The default setting is backwards
       compatible to avoid the infinetisimal possibility of breaking existing
       LMTP-based content filters.

lmtp_bind_address (default: empty)
       The LMTP-specific version of the smtp_bind_address configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_bind_address6 (default: empty)
       The LMTP-specific version of the smtp_bind_address6 configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_body_checks (default: empty)
       The LMTP-specific version of the smtp_body_checks configuration
       parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_cache_connection (default: yes)
       Keep Postfix LMTP client connections open for up to $max_idle seconds.
       When the LMTP client receives a request for the same connection the
       connection is reused.

       This parameter is available in Postfix version 2.2 and earlier.  With
       Postfix version 2.3 and later, see lmtp_connection_cache_on_demand,
       lmtp_connection_cache_destinations, or
       lmtp_connection_reuse_time_limit.

       The effectiveness of cached connections will be determined by the
       number of LMTP servers in use, and the concurrency limit specified for
       the LMTP client. Cached connections are closed under any of the
       following conditions:

       o      The LMTP client idle time limit is reached.  This limit is
              specified with the Postfix max_idle configuration parameter.

       o      A delivery request specifies a different destination than the
              one currently cached.

       o      The per-process limit on the number of delivery requests is
              reached.  This limit is specified with the Postfix max_use
              configuration parameter.

       o      Upon the onset of another delivery request, the LMTP server
              associated with the current session does not respond to the RSET
              command.

       Most of these limitations will be removed after Postfix implements a
       connection cache that is shared among multiple LMTP client programs.

lmtp_cname_overrides_servername (default: yes)
       The LMTP-specific version of the smtp_cname_overrides_servername
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connect_timeout (default: 0s)
       The LMTP client time limit for completing a TCP connection, or zero
       (use the operating system built-in time limit).  When no connection can
       be made within the deadline, the LMTP client tries the next address on
       the mail exchanger list.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       Example:

       lmtp_connect_timeout = 30s

lmtp_connection_cache_destinations (default: empty)
       The LMTP-specific version of the smtp_connection_cache_destinations
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_on_demand (default: yes)
       The LMTP-specific version of the smtp_connection_cache_on_demand
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_time_limit (default: 2s)
       The LMTP-specific version of the smtp_connection_cache_time_limit
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_reuse_time_limit (default: 300s)
       The LMTP-specific version of the smtp_connection_reuse_time_limit
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_data_done_timeout (default: 600s)
       The LMTP client time limit for sending the LMTP ".", and for receiving
       the server response.  When no response is received within the deadline,
       a warning is logged that the mail may be delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_data_init_timeout (default: 120s)
       The LMTP client time limit for sending the LMTP DATA command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_data_xfer_timeout (default: 180s)
       The LMTP client time limit for sending the LMTP message content.  When
       the connection stalls for more than $lmtp_data_xfer_timeout the LMTP
       client terminates the transfer.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_defer_if_no_mx_address_found (default: no)
       The LMTP-specific version of the smtp_defer_if_no_mx_address_found
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_destination_concurrency_limit (default:
$default_destination_concurrency_limit)
       The maximal number of parallel deliveries to the same destination via
       the lmtp message delivery transport. This limit is enforced by the
       queue manager. The message delivery transport name is the first field
       in the entry in the master.cf file.

lmtp_destination_recipient_limit (default:
$default_destination_recipient_limit)
       The maximal number of recipients per message for the lmtp message
       delivery transport. This limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of
       lmtp_destination_concurrency_limit from concurrency per domain into
       concurrency per recipient.

lmtp_discard_lhlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote LMTP server address, with case
       insensitive lists of LHLO keywords (pipelining, starttls, auth, etc.)
       that the LMTP client will ignore in the LHLO response from a remote
       LMTP server. See lmtp_discard_lhlo_keywords for details. The table is
       not indexed by hostname for consistency with
       smtpd_discard_ehlo_keyword_address_maps.

       This feature is available in Postfix 2.3 and later.

lmtp_discard_lhlo_keywords (default: empty)
       A case insensitive list of LHLO keywords (pipelining, starttls, auth,
       etc.) that the LMTP client will ignore in the LHLO response from a
       remote LMTP server.

       This feature is available in Postfix 2.3 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

       o      Use the lmtp_discard_lhlo_keyword_address_maps feature to
              discard LHLO keywords selectively.

lmtp_dns_resolver_options (default: empty)
       The LMTP-specific version of the smtp_dns_resolver_options
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_enforce_tls (default: no)
       The LMTP-specific version of the smtp_enforce_tls configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_generic_maps (default: empty)
       The LMTP-specific version of the smtp_generic_maps configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_header_checks (default: empty)
       The LMTP-specific version of the smtp_header_checks configuration
       parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_host_lookup (default: dns)
       The LMTP-specific version of the smtp_host_lookup configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_name (default: $myhostname)
       The hostname to send in the LMTP LHLO command.

       The default value is the machine hostname.  Specify a hostname or
       [ip.add.re.ss].

       This information can be specified in the main.cf file for all LMTP
       clients, or it can be specified in the master.cf file for a specific
       client, for example:

           /etc/postfix/master.cf:
               mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_timeout (default: 300s)
       The LMTP client time limit for sending the LHLO command, and for
       receiving the initial server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_line_length_limit (default: 990)
       The LMTP-specific version of the smtp_line_length_limit configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mail_timeout (default: 300s)
       The LMTP client time limit for sending the MAIL FROM command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_mime_header_checks (default: empty)
       The LMTP-specific version of the smtp_mime_header_checks configuration
       parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_mx_address_limit (default: 5)
       The LMTP-specific version of the smtp_mx_address_limit configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mx_session_limit (default: 2)
       The LMTP-specific version of the smtp_mx_session_limit configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_nested_header_checks (default: empty)
       The LMTP-specific version of the smtp_nested_header_checks
       configuration parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_pix_workaround_delay_time (default: 10s)
       The LMTP-specific version of the smtp_pix_workaround_delay_time
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_maps (default: empty)
       The LMTP-specific version of the smtp_pix_workaround_maps configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_pix_workaround_threshold_time (default: 500s)
       The LMTP-specific version of the smtp_pix_workaround_threshold_time
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workarounds (default: empty)
       The LMTP-specific version of the smtp_pix_workaround configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_quit_timeout (default: 300s)
       The LMTP client time limit for sending the QUIT command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_quote_rfc821_envelope (default: yes)
       The LMTP-specific version of the smtp_quote_rfc821_envelope
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_randomize_addresses (default: yes)
       The LMTP-specific version of the smtp_randomize_addresses configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_rcpt_timeout (default: 300s)
       The LMTP client time limit for sending the RCPT TO command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_reply_filter (default: empty)
       The LMTP-specific version of the smtp_reply_filter configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_rset_timeout (default: 20s)
       The LMTP client time limit for sending the RSET command, and for
       receiving the server response. The LMTP client sends RSET in order to
       finish a recipient address probe, or to verify that a cached connection
       is still alive.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_sasl_auth_cache_name (default: empty)
       The LMTP-specific version of the smtp_sasl_auth_cache_name
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_cache_time (default: 90d)
       The LMTP-specific version of the smtp_sasl_auth_cache_time
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix LMTP client.

lmtp_sasl_auth_soft_bounce (default: yes)
       The LMTP-specific version of the smtp_sasl_auth_soft_bounce
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_mechanism_filter (default: empty)
       The LMTP-specific version of the smtp_sasl_mechanism_filter
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_password_maps (default: empty)
       Optional LMTP client lookup tables with one username:password entry per
       host or domain.  If a remote host or domain has no username:password
       entry, then the Postfix LMTP client will not attempt to authenticate to
       the remote host.

lmtp_sasl_path (default: empty)
       Implementation-specific information that is passed through to the SASL
       plug-in implementation that is selected with lmtp_sasl_type.  Typically
       this specifies the name of a configuration file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_security_options (default: noplaintext, noanonymous)
       SASL security options; as of Postfix 2.3 the list of available features
       depends on the SASL client implementation that is selected with
       lmtp_sasl_type.

       The following security features are defined for the cyrus client SASL
       implementation:

       noplaintext
              Disallow authentication methods that use plaintext passwords.

       noactive
              Disallow authentication methods that are vulnerable to non-
              dictionary active attacks.

       nodictionary
              Disallow authentication methods that are vulnerable to passive
              dictionary attack.

       noanonymous
              Disallow anonymous logins.

       Example:

       lmtp_sasl_security_options = noplaintext

lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)
       The LMTP-specific version of the smtp_sasl_tls_security_options
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_tls_verified_security_options (default:
$lmtp_sasl_tls_security_options)
       The LMTP-specific version of the
       smtp_sasl_tls_verified_security_options configuration parameter.  See
       there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_type (default: cyrus)
       The SASL plug-in type that the Postfix LMTP client should use for
       authentication.  The available types are listed with the "postconf -A"
       command.

       This feature is available in Postfix 2.3 and later.

lmtp_send_xforward_command (default: no)
       Send an XFORWARD command to the LMTP server when the LMTP LHLO server
       response announces XFORWARD support.  This allows an lmtp(8) delivery
       agent, used for content filter message injection, to forward the name,
       address, protocol and HELO name of the original client to the content
       filter and downstream queuing LMTP server.  Before you change the value
       to yes, it is best to make sure that your content filter supports this
       command.

       This feature is available in Postfix 2.1 and later.

lmtp_sender_dependent_authentication (default: no)
       The LMTP-specific version of the smtp_sender_dependent_authentication
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_5xx_greeting (default: yes)
       The LMTP-specific version of the smtp_skip_5xx_greeting configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_quit_response (default: no)
       Wait for the response to the LMTP QUIT command.

lmtp_starttls_timeout (default: 300s)
       The LMTP-specific version of the smtp_starttls_timeout configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tcp_port (default: 24)
       The default TCP port that the Postfix LMTP client connects to.

lmtp_tls_CAfile (default: empty)
       The LMTP-specific version of the smtp_tls_CAfile configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_CApath (default: empty)
       The LMTP-specific version of the smtp_tls_CApath configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_block_early_mail_reply (default: empty)
       The LMTP-specific version of the smtp_tls_block_early_mail_reply
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_tls_cert_file (default: empty)
       The LMTP-specific version of the smtp_tls_cert_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_ciphers (default: export)
       The LMTP-specific version of the smtp_tls_ciphers configuration
       parameter. See there for details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_dcert_file (default: empty)
       The LMTP-specific version of the smtp_tls_dcert_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)
       The LMTP-specific version of the smtp_tls_dkey_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_eccert_file (default: empty)
       The LMTP-specific version of the smtp_tls_eccert_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_eckey_file (default: empty)
       The LMTP-specific version of the smtp_tls_eckey_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_enforce_peername (default: yes)
       The LMTP-specific version of the smtp_tls_enforce_peername
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_exclude_ciphers (default: empty)
       The LMTP-specific version of the smtp_tls_exclude_ciphers configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_fingerprint_cert_match (default: empty)
       The LMTP-specific version of the smtp_tls_fingerprint_cert_match
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_fingerprint_digest (default: md5)
       The LMTP-specific version of the smtp_tls_fingerprint_digest
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_key_file (default: $lmtp_tls_cert_file)
       The LMTP-specific version of the smtp_tls_key_file configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_loglevel (default: 0)
       The LMTP-specific version of the smtp_tls_loglevel configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_ciphers (default: empty)
       The LMTP-specific version of the smtp_tls_mandatory_ciphers
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_exclude_ciphers (default: empty)
       The LMTP-specific version of the smtp_tls_mandatory_exclude_ciphers
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_protocols (default: !SSLv2)
       The LMTP-specific version of the smtp_tls_mandatory_protocols
       configuration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_note_starttls_offer (default: no)
       The LMTP-specific version of the smtp_tls_note_starttls_offer
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_per_site (default: empty)
       The LMTP-specific version of the smtp_tls_per_site configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_policy_maps (default: empty)
       The LMTP-specific version of the smtp_tls_policy_maps configuration
       parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_protocols (default: empty)
       The LMTP-specific version of the smtp_tls_protocols configuration
       parameter. See there for details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_scert_verifydepth (default: 9)
       The LMTP-specific version of the smtp_tls_scert_verifydepth
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_secure_cert_match (default: nexthop)
       The LMTP-specific version of the smtp_tls_secure_cert_match
       configuration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_security_level (default: empty)
       The LMTP-specific version of the smtp_tls_security_level configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_database (default: empty)
       The LMTP-specific version of the smtp_tls_session_cache_database
       configuration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_timeout (default: 3600s)
       The LMTP-specific version of the smtp_tls_session_cache_timeout
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_verify_cert_match (default: hostname)
       The LMTP-specific version of the smtp_tls_verify_cert_match
       configuration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_use_tls (default: no)
       The LMTP-specific version of the smtp_use_tls configuration parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_xforward_timeout (default: 300s)
       The LMTP client time limit for sending the XFORWARD command, and for
       receiving the server response.

       In case of problems the client does NOT try the next address on the
       mail exchanger list.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

local_command_shell (default: empty)
       Optional shell program for local(8) delivery to non-Postfix command.
       By default, non-Postfix commands are executed directly; commands are
       given to given to the default shell (typically, /bin/sh) only when they
       contain shell meta characters or shell built-in commands.

       "sendmail's restricted shell" (smrsh) is what most people will use in
       order to restrict what programs can be run from e.g. .forward files
       (smrsh is part of the Sendmail distribution).

       Note: when a shell program is specified, it is invoked even when the
       command contains no shell built-in commands or meta characters.

       Example:

       local_command_shell = /some/where/smrsh -c
       local_command_shell = /bin/bash -c

local_destination_concurrency_limit (default: 2)
       The maximal number of parallel deliveries via the local mail delivery
       transport to the same recipient (when
       "local_destination_recipient_limit = 1") or the maximal number of
       parallel deliveries to the same local domain (when
       "local_destination_recipient_limit > 1"). This limit is enforced by the
       queue manager. The message delivery transport name is the first field
       in the entry in the master.cf file.

       A low limit of 2 is recommended, just in case someone has an expensive
       shell command in a .forward file or in an alias (e.g., a mailing list
       manager).  You don't want to run lots of those at the same time.

local_destination_recipient_limit (default: 1)
       The maximal number of recipients per message delivery via the local
       mail delivery transport. This limit is enforced by the queue manager.
       The message delivery transport name is the first field in the entry in
       the master.cf file.

       Setting this parameter to a value > 1 changes the meaning of
       local_destination_concurrency_limit from concurrency per recipient into
       concurrency per domain.

local_header_rewrite_clients (default: permit_inet_interfaces)
       Rewrite message header addresses in mail from these clients and update
       incomplete addresses with the domain name in $myorigin or $mydomain;
       either don't rewrite message headers from other clients at all, or
       rewrite message headers and update incomplete addresses with the domain
       specified in the remote_header_rewrite_domain parameter.

       See the append_at_myorigin and append_dot_mydomain parameters for
       details of how domain names are appended to incomplete addresses.

       Specify a list of zero or more of the following:

       permit_inet_interfaces
              Append the domain name in $myorigin or $mydomain when the client
              IP address matches $inet_interfaces. This is enabled by default.

       permit_mynetworks
              Append the domain name in $myorigin or $mydomain when the client
              IP address matches any network or network address listed in
              $mynetworks. This setting will not prevent remote mail header
              address rewriting when mail from a remote client is forwarded by
              a neighboring system.

       permit_sasl_authenticated
              Append the domain name in $myorigin or $mydomain when the client
              is successfully authenticated via the RFC 4954 (AUTH) protocol.

       permit_tls_clientcerts
              Append the domain name in $myorigin or $mydomain when the client
              TLS certificate fingerprint is listed in $relay_clientcerts.
              The fingerprint digest algorithm is configurable via the
              smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior
              to Postfix version 2.5).

       permit_tls_all_clientcerts
              Append the domain name in $myorigin or $mydomain when the client
              TLS certificate is successfully verified, regardless of whether
              it is listed on the server, and regardless of the certifying
              authority.

       check_address_map type:table

       type:table
              Append the domain name in $myorigin or $mydomain when the client
              IP address matches the specified lookup table.  The lookup
              result is ignored, and no subnet lookup is done. This is
              suitable for, e.g., pop-before-smtp lookup tables.

       Examples:

       The Postfix < 2.2 backwards compatible setting: always rewrite message
       headers, and always append my own domain to incomplete header
       addresses.

           local_header_rewrite_clients = static:all

       The purist (and default) setting: rewrite headers only in mail from
       Postfix sendmail and in SMTP mail from this machine.

           local_header_rewrite_clients = permit_inet_interfaces

       The intermediate setting: rewrite header addresses and append $myorigin
       or $mydomain information only with mail from Postfix sendmail, from
       local clients, or from authorized SMTP clients.

       Note: this setting will not prevent remote mail header address
       rewriting when mail from a remote client is forwarded by a neighboring
       system.

           local_header_rewrite_clients = permit_mynetworks,
               permit_sasl_authenticated permit_tls_clientcerts
               check_address_map hash:/etc/postfix/pop-before-smtp

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
       Lookup tables with all names or addresses of local recipients: a
       recipient address is local when its domain matches $mydestination,
       $inet_interfaces or $proxy_interfaces.  Specify @domain as a wild-card
       for domains that do not have a valid recipient list.  Technically,
       tables listed with $local_recipient_maps are used as lists: Postfix
       needs to know only if a lookup string is found or not, but it does not
       use the result from table lookup.

       If this parameter is non-empty (the default), then the Postfix SMTP
       server will reject mail for unknown local users.

       To turn off local recipient checking in the Postfix SMTP server,
       specify "local_recipient_maps =" (i.e. empty).

       The default setting assumes that you use the default Postfix local
       delivery agent for local delivery. You need to update the
       local_recipient_maps setting if:

       o      You redefine the local delivery agent in master.cf.

       o      You redefine the "local_transport" setting in main.cf.

       o      You use the "luser_relay", "mailbox_transport", or
              "fallback_transport" feature of the Postfix local(8) delivery
              agent.

       Details are described in the LOCAL_RECIPIENT_README file.

       Beware: if the Postfix SMTP server runs chrooted, you need to access
       the passwd file via the proxymap(8) service, in order to overcome
       chroot access restrictions. The alternative, maintaining a copy of the
       system password file in the chroot jail is not practical.

       Examples:

       local_recipient_maps =

local_transport (default: local:$myhostname)
       The default mail delivery transport and next-hop destination for final
       delivery to domains listed with mydestination, and for [ipaddress]
       destinations that match $inet_interfaces or $proxy_interfaces.  This
       information can be overruled with the transport(5) table.

       By default, local mail is delivered to the transport called "local",
       which is just the name of a service that is defined the master.cf file.

       Specify a string of the form transport:nexthop, where transport is the
       name of a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       Beware: if you override the default local delivery agent then you need
       to review the LOCAL_RECIPIENT_README document, otherwise the SMTP
       server may reject mail for local recipients.

luser_relay (default: empty)
       Optional catch-all destination for unknown local(8) recipients.  By
       default, mail for unknown recipients in domains that match
       $mydestination, $inet_interfaces or $proxy_interfaces is returned as
       undeliverable.

       The following $name expansions are done on luser_relay:

       $domain
              The recipient domain.

       $extension
              The recipient address extension.

       $home  The recipient's home directory.

       $local The entire recipient address localpart.

       $recipient
              The full recipient address.

       $recipient_delimiter
              The system-wide recipient address extension delimiter.

       $shell The recipient's login shell.

       $user  The recipient username.

       ${name?value}
              Expands to value when $name has a non-empty value.

       ${name:value}
              Expands to value when $name has an empty value.

       Instead of $name you can also specify ${name} or $(name).

       Note: luser_relay works only for the Postfix local(8) delivery agent.

       Note: if you use this feature for accounts not in the UNIX password
       file, then you must specify "local_recipient_maps =" (i.e. empty) in
       the main.cf file, otherwise the Postfix SMTP server will reject mail
       for non-UNIX accounts with "User unknown in local recipient table".

       Examples:

       luser_relay = $userATother.host
       luser_relay = $localATother.host
       luser_relay = admin+$local

mail_name (default: Postfix)
       The mail system name that is displayed in Received: headers, in the
       SMTP greeting banner, and in bounced mail.

mail_owner (default: postfix)
       The UNIX system account that owns the Postfix queue and most Postfix
       daemon processes.  Specify the name of a user account that does not
       share a group with other accounts and that owns no other files or
       processes on the system.  In particular, don't specify nobody or
       daemon.  PLEASE USE A DEDICATED USER ID AND GROUP ID.

       When this parameter value is changed you need to re-run "postfix set-
       permissions" (with Postfix version 2.0 and earlier: "/etc/postfix/post-
       install set-permissions".

mail_release_date (default: see postconf -d output)
       The Postfix release date, in "YYYYMMDD" format.

mail_spool_directory (default: see postconf -d output)
       The directory where local(8) UNIX-style mailboxes are kept. The default
       setting depends on the system type. Specify a name ending in / for
       maildir-style delivery.

       Note: maildir delivery is done with the privileges of the recipient.
       If you use the mail_spool_directory setting for maildir style delivery,
       then you must create the top-level maildir directory in advance.
       Postfix will not create it.

       Examples:

       mail_spool_directory = /var/mail
       mail_spool_directory = /var/spool/mail

mail_version (default: see postconf -d output)
       The version of the mail system. Stable releases are named
       major.minor.patchlevel. Experimental releases also include the release
       date. The version string can be used in, for example, the SMTP greeting
       banner.

mailbox_command (default: empty)
       Optional external command that the local(8) delivery agent should use
       for mailbox delivery.  The command is run with the user ID and the
       primary group ID privileges of the recipient.  Exception: command
       delivery for root executes with $default_privs privileges.  This is not
       a problem, because 1) mail for root should always be aliased to a real
       user and 2) don't log in as root, use "su" instead.

       The following environment variables are exported to the command:

       CLIENT_ADDRESS
              Remote client network address. Available in Postfix version 2.2
              and later.

       CLIENT_HELO
              Remote client EHLO command parameter. Available in Postfix
              version 2.2 and later.

       CLIENT_HOSTNAME
              Remote client hostname. Available in Postfix version 2.2 and
              later.

       CLIENT_PROTOCOL
              Remote client protocol. Available in Postfix version 2.2 and
              later.

       DOMAIN The domain part of the recipient address.

       EXTENSION
              The optional address extension.

       HOME   The recipient home directory.

       LOCAL  The recipient address localpart.

       LOGNAME
              The recipient's username.

       ORIGINAL_RECIPIENT
              The entire recipient address, before any address rewriting or
              aliasing.

       RECIPIENT
              The full recipient address.

       SASL_METHOD
              SASL authentication method specified in the remote client AUTH
              command. Available in Postfix version 2.2 and later.

       SASL_SENDER
              SASL sender address specified in the remote client MAIL FROM
              command. Available in Postfix version 2.2 and later.

       SASL_USER
              SASL username specified in the remote client AUTH command.
              Available in Postfix version 2.2 and later.

       SENDER The full sender address.

       SHELL  The recipient's login shell.

       USER   The recipient username.

       Unlike other Postfix configuration parameters, the mailbox_command
       parameter is not subjected to $name substitutions. This is to make it
       easier to specify shell syntax (see example below).

       If you can, avoid shell meta characters because they will force Postfix
       to run an expensive shell process. If you're delivering via Procmail
       then running a shell won't make a noticeable difference in the total
       cost.

       Note: if you use the mailbox_command feature to deliver mail system-
       wide, you must set up an alias that forwards mail for root to a real
       user.

       The precedence of local(8) delivery features from high to low is:
       aliases, .forward files, mailbox_transport_maps, mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,
       mail_spool_directory, fallback_transport_maps, fallback_transport and
       luser_relay.

       Examples:

       mailbox_command = /some/where/procmail
       mailbox_command = /some/where/procmail -a "$EXTENSION"
       mailbox_command = /some/where/maildrop -d "$USER"
               -f "$SENDER" "$EXTENSION"

mailbox_command_maps (default: empty)
       Optional lookup tables with per-recipient external commands to use for
       local(8) mailbox delivery.  Behavior is as with mailbox_command.

       The precedence of local(8) delivery features from high to low is:
       aliases, .forward files, mailbox_transport_maps, mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,
       mail_spool_directory, fallback_transport_maps, fallback_transport and
       luser_relay.

mailbox_delivery_lock (default: see postconf -d output)
       How to lock a UNIX-style local(8) mailbox before attempting delivery.
       For a list of available file locking methods, use the "postconf -l"
       command.

       This setting is ignored with maildir style delivery, because such
       deliveries are safe without explicit locks.

       Note: The dotlock method requires that the recipient UID or GID has
       write access to the parent directory of the mailbox file.

       Note: the default setting of this parameter is system dependent.

mailbox_size_limit (default: 51200000)
       The maximal size of any local(8) individual mailbox or maildir file, or
       zero (no limit).  In fact, this limits the size of any file that is
       written to upon local delivery, including files written by external
       commands that are executed by the local(8) delivery agent.

       This limit must not be smaller than the message size limit.

mailbox_transport (default: empty)
       Optional message delivery transport that the local(8) delivery agent
       should use for mailbox delivery to all local recipients, whether or not
       they are found in the UNIX passwd database.

       The precedence of local(8) delivery features from high to low is:
       aliases, .forward files, mailbox_transport_maps, mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,
       mail_spool_directory, fallback_transport_maps, fallback_transport and
       luser_relay.

mailbox_transport_maps (default: empty)
       Optional lookup tables with per-recipient message delivery transports
       to use for local(8) mailbox delivery, whether or not the recipients are
       found in the UNIX passwd database.

       The precedence of local(8) delivery features from high to low is:
       aliases, .forward files, mailbox_transport_maps, mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,
       mail_spool_directory, fallback_transport_maps, fallback_transport and
       luser_relay.

       For safety reasons, this feature does not allow $number substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

mailq_path (default: see postconf -d output)
       Sendmail compatibility feature that specifies where the Postfix
       mailq(1) command is installed. This command can be used to list the
       Postfix mail queue.

manpage_directory (default: see postconf -d output)
       Where the Postfix manual pages are installed.

maps_rbl_domains (default: empty)
       Obsolete feature: use the reject_rbl_client feature instead.

maps_rbl_reject_code (default: 554)
       The numerical Postfix SMTP server response code when a remote SMTP
       client request is blocked by the reject_rbl_client,
       reject_rhsbl_client, reject_rhsbl_reverse_client, reject_rhsbl_sender
       or reject_rhsbl_recipient restriction.

       Do not change this unless you have a complete understanding of RFC
       2821.

masquerade_classes (default: envelope_sender, header_sender, header_recipient)
       What addresses are subject to address masquerading.

       By default, address masquerading is limited to envelope sender
       addresses, and to header sender and header recipient addresses.  This
       allows you to use address masquerading on a mail gateway while still
       being able to forward mail to users on individual machines.

       Specify zero or more of: envelope_sender, envelope_recipient,
       header_sender, header_recipient

masquerade_domains (default: empty)
       Optional list of domains whose subdomain structure will be stripped off
       in email addresses.

       The list is processed left to right, and processing stops at the first
       match.  Thus,

           masquerade_domains = foo.example.com example.com

       strips "userATany.com" to "userATfoo.com", but
       strips "userATany.com" to "userATexample.com".

       A domain name prefixed with ! means do not masquerade this domain or
       its subdomains. Thus,

           masquerade_domains = !foo.example.com example.com

       does not change "userATany.com" or
       "userATfoo.com", but strips "userATany.com" to
       "userATexample.com".

       Note: with Postfix version 2.2, message header address masquerading
       happens only when message header address rewriting is enabled:

       o      The message is received with the Postfix sendmail(1) command,

       o      The message is received from a network client that matches
              $local_header_rewrite_clients,

       o      The message is received from the network, and the
              remote_header_rewrite_domain parameter specifies a non-empty
              value.

       To get the behavior before Postfix version 2.2, specify
       "local_header_rewrite_clients = static:all".

       Example:

       masquerade_domains = $mydomain

masquerade_exceptions (default: empty)
       Optional list of user names that are not subjected to address
       masquerading, even when their address matches $masquerade_domains.

       By default, address masquerading makes no exceptions.

       Specify a list of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The list is matched left to
       right, and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude a name from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

       Examples:

       masquerade_exceptions = root, mailer-daemon
       masquerade_exceptions = root

master_service_disable (default: empty)
       Selectively disable master(8) listener ports by service type or by
       service name and type.  Specify a list of service types ("inet",
       "unix", "fifo", or "pass") or "name.type" tuples, where "name" is the
       first field of a master.cf entry and "type" is a service type. As with
       other Postfix matchlists, a search stops at the first match.  Specify
       "!pattern" to exclude a service from the list. By default, all
       master(8) listener ports are enabled.

       Note: this feature does not support "/file/name" or "type:table"
       patterns, nor does it support wildcards such as "*" or "all". This is
       intentional.

       Examples:

       # Turn on all master(8) listener ports (the default).
       master_service_disable =
       # Turn off only the main SMTP listener port.
       master_service_disable = smtp.inet
       # Turn off all TCP/IP listener ports.
       master_service_disable = inet
       # Turn off all TCP/IP listener ports except "foo".
       master_service_disable = !foo.inet, inet

       This feature is available in Postfix 2.6 and later.

max_idle (default: 100s)
       The maximum amount of time that an idle Postfix daemon process waits
       for an incoming connection before terminating voluntarily.  This
       parameter is ignored by the Postfix queue manager and by other long-
       lived Postfix daemon processes.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

max_use (default: 100)
       The maximal number of incoming connections that a Postfix daemon
       process will service before terminating voluntarily.  This parameter is
       ignored by the Postfix queue manager and by other long-lived Postfix
       daemon processes.

maximal_backoff_time (default: 4000s)
       The maximal time between attempts to deliver a deferred message.

       This parameter should be set to a value greater than or equal to
       $minimal_backoff_time. See also $queue_run_delay.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

maximal_queue_lifetime (default: 5d)
       The maximal time a message is queued before it is sent back as
       undeliverable.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is d (days).

       Specify 0 when mail delivery should be tried only once.

message_reject_characters (default: empty)
       The set of characters that Postfix will reject in message content.  The
       usual C-like escape sequences are recognized: \a \b \f \n \r \t \v \ddd
       (up to three octal digits) and \\.

       Example:

       message_reject_characters = \0

       This feature is available in Postfix 2.3 and later.

message_size_limit (default: 10240000)
       The maximal size in bytes of a message, including envelope information.

       Note: be careful when making changes.  Excessively small values will
       result in the loss of non-delivery notifications, when a bounce message
       size exceeds the local or remote MTA's message size limit.

message_strip_characters (default: empty)
       The set of characters that Postfix will remove from message content.
       The usual C-like escape sequences are recognized: \a \b \f \n \r \t \v
       \ddd (up to three octal digits) and \\.

       Example:

       message_strip_characters = \0

       This feature is available in Postfix 2.3 and later.

milter_command_timeout (default: 30s)
       The time limit for sending an SMTP command to a Milter (mail filter)
       application, and for receiving the response.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_connect_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after
       completion of an SMTP connection. See MILTER_README for a list of
       available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_connect_timeout (default: 30s)
       The time limit for connecting to a Milter (mail filter) application,
       and for negotiating protocol options.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_content_timeout (default: 300s)
       The time limit for sending message content to a Milter (mail filter)
       application, and for receiving the response.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_data_macros (default: see postconf -d output)
       The macros that are sent to version 4 or higher Milter (mail filter)
       applications after the SMTP DATA command. See MILTER_README for a list
       of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_default_action (default: tempfail)
       The default action when a Milter (mail filter) application is
       unavailable or mis-configured. Specify one of the following:

       accept Proceed as if the mail filter was not present.

       reject Reject all further commands in this session with a permanent
              status code.

       tempfail
              Reject all further commands in this session with a temporary
              status code.

       quarantine
              Like "accept", but freeze the message in the "hold" queue.
              Available with Postfix 2.6 and later.

       This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       message end-of-data. See MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_end_of_header_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       end of the message header. See MILTER_README for a list of available
       macro names and their meanings.

       This feature is available in Postfix 2.5 and later.

milter_header_checks (default: empty)
       Optional lookup tables for content inspection of message headers that
       are produced by Milter applications.  See the header_checks(5) manual
       page available actions. Currently, PREPEND is not implemented.

       The following example sends all mail that is marked as SPAM to a spam
       handling machine. Note that matches are case-insensitive by default.

       /etc/postfix/main.cf:
           milter_header_checks = pcre:/etc/postfix/milter_header_checks

       /etc/postfix/milter_header_checks:
           /^X-SPAM-FLAG:\s+YES/ FILTER mysmtp:sanitizer.example.com:25

       The milter_header_checks mechanism could also be used for whitelisting.
       For example it could be used to skip heavy content inspection for DKIM-
       signed mail from known friendly domains.

       This feature is available in Postfix 2.7, and as an optional patch for
       Postfix 2.6.

milter_helo_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP HELO or EHLO command. See MILTER_README for a list of available
       macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_daemon_name (default: $myhostname)
       The {daemon_name} macro value for Milter (mail filter) applications.
       See MILTER_README for a list of available macro names and their
       meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_v (default: $mail_name $mail_version)
       The {v} macro value for Milter (mail filter) applications.  See
       MILTER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_mail_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP MAIL FROM command. See MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_protocol (default: 6)
       The mail filter protocol version and optional protocol extensions for
       communication with a Milter application; prior to Postfix 2.6 the
       default protocol is 2. Postfix sends this version number during the
       initial protocol handshake.  It should match the version number that is
       expected by the mail filter application (or by its Milter library).

       Protocol versions:

       2      Use Sendmail 8 mail filter protocol version 2 (default with
              Sendmail version 8.11 .. 8.13 and Postfix version 2.3 ..  2.5).

       3      Use Sendmail 8 mail filter protocol version 3.

       4      Use Sendmail 8 mail filter protocol version 4.

       6      Use Sendmail 8 mail filter protocol version 6 (default with
              Sendmail version 8.14 and Postfix version 2.6).

       Protocol extensions:

       no_header_reply
              Specify this when the Milter application will not reply for each
              individual message header.

       This feature is available in Postfix 2.3 and later.

milter_rcpt_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP RCPT TO command. See MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_unknown_command_macros (default: see postconf -d output)
       The macros that are sent to version 3 or higher Milter (mail filter)
       applications after an unknown SMTP command.  See MILTER_README for a
       list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

mime_boundary_length_limit (default: 2048)
       The maximal length of MIME multipart boundary strings. The MIME
       processor is unable to distinguish between boundary strings that do not
       differ in the first $mime_boundary_length_limit characters.

       This feature is available in Postfix 2.0 and later.

mime_header_checks (default: $header_checks)
       Optional lookup tables for content inspection of MIME related message
       headers, as described in the header_checks(5) manual page.

       This feature is available in Postfix 2.0 and later.

mime_nesting_limit (default: 100)
       The maximal recursion level that the MIME processor will handle.
       Postfix refuses mail that is nested deeper than the specified limit.

       This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 300s)
       The minimal time between attempts to deliver a deferred message; prior
       to Postfix 2.4 the default value was 1000s.

       This parameter also limits the time an unreachable destination is kept
       in the short-term, in-memory, destination status cache.

       This parameter should be set greater than or equal to $queue_run_delay.
       See also $maximal_backoff_time.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

multi_instance_directories (default: empty)
       An optional list of non-default Postfix configuration directories;
       these directories belong to additional Postfix instances that share the
       Postfix executable files and documentation with the default Postfix
       instance, and that are started, stopped, etc., together with the
       default Postfix instance.  Specify a list of pathnames separated by
       comma or whitespace.

       When $multi_instance_directories is empty, the postfix(1) command runs
       in single-instance mode and operates on a single Postfix instance only.
       Otherwise, the postfix(1) command runs in multi-instance mode and
       invokes the multi-instance manager specified with the
       multi_instance_wrapper parameter. The multi-instance manager in turn
       executes postfix(1) commands for the default instance and for all
       Postfix instances in $multi_instance_directories.

       Currently, this parameter setting is ignored except for the default
       main.cf file.

       This feature is available in Postfix 2.6 and later.

multi_instance_enable (default: no)
       Allow this Postfix instance to be started, stopped, etc., by a multi-
       instance manager.  By default, new instances are created in a safe
       state that prevents them from being started inadvertently.  This
       parameter is reserved for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_group (default: empty)
       The optional instance group name of this Postfix instance. A group
       identifies closely-related Postfix instances that the multi-instance
       manager can start, stop, etc., as a unit.  This parameter is reserved
       for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_name (default: empty)
       The optional instance name of this Postfix instance. This name becomes
       also the default value for the syslog_name parameter.

       This feature is available in Postfix 2.6 and later.

multi_instance_wrapper (default: empty)
       The pathname of a multi-instance manager command that the postfix(1)
       command invokes when the multi_instance_directories parameter value is
       non-empty. The pathname may be followed by initial command arguments
       separated by whitespace; shell metacharacters such as quotes are not
       supported in this context.

       The postfix(1) command invokes the manager command with the postfix(1)
       non-option command arguments on the manager command line, and with all
       installation configuration parameters exported into the manager command
       process environment. The manager command in turn invokes the postfix(1)
       command for individual Postfix instances as "postfix -c
       config_directory command".

       This feature is available in Postfix 2.6 and later.

multi_recipient_bounce_reject_code (default: 550)
       The numerical Postfix SMTP server response code when a remote SMTP
       client request is blocked by the reject_multi_recipient_bounce
       restriction.

       Do not change this unless you have a complete understanding of RFC
       2821.

       This feature is available in Postfix 2.1 and later.

mydestination (default: $myhostname, localhost.$mydomain, localhost)
       The list of domains that are delivered via the $local_transport mail
       delivery transport. By default this is the Postfix local(8) delivery
       agent which looks up all recipients in /etc/passwd and /etc/aliases.
       The SMTP server validates recipient addresses with
       $local_recipient_maps and rejects non-existent recipients. See also the
       local domain class in the ADDRESS_CLASS_README file.

       The default mydestination value specifies names for the local machine
       only.  On a mail domain gateway, you should also include $mydomain.

       The $local_transport delivery method is also selected for mail
       addressed to user@[the.net.work.address] of the mail system (the IP
       addresses specified with the inet_interfaces and proxy_interfaces
       parameters).

       Warnings:

       o      Do not specify the names of virtual domains - those domains are
              specified elsewhere. See VIRTUAL_README for more information.

       o      Do not specify the names of domains that this machine is backup
              MX host for. See STANDARD_CONFIGURATION_README for how to set up
              backup MX hosts.

       o      By default, the Postfix SMTP server rejects mail for recipients
              not listed with the local_recipient_maps parameter.  See the
              postconf(5) manual for a description of the local_recipient_maps
              and unknown_local_recipient_reject_code parameters.

       Specify a list of host or domain names, "/file/name" or "type:table"
       patterns, separated by commas and/or whitespace. A "/file/name" pattern
       is replaced by its contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.

       Examples:

       mydestination = $myhostname, localhost.$mydomain $mydomain
       mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

mydomain (default: see postconf -d output)
       The internet domain name of this mail system.  The default is to use
       $myhostname minus the first component, or "localdomain" (Postfix 2.3
       and later).  $mydomain is used as a default value for many other
       configuration parameters.

       Example:

       mydomain = domain.tld

myhostname (default: see postconf -d output)
       The internet hostname of this mail system. The default is to use the
       fully-qualified domain name (FQDN) from gethostname(), or to use the
       non-FQDN result from gethostname() and append ".$mydomain".
       $myhostname is used as a default value for many other configuration
       parameters.

       Example:

       myhostname = host.example.com

mynetworks (default: see postconf -d output)
       The list of "trusted" SMTP clients that have more privileges than
       "strangers".

       In particular, "trusted" SMTP clients are allowed to relay mail through
       Postfix.  See the smtpd_recipient_restrictions parameter description in
       the postconf(5) manual.

       You can specify the list of "trusted" network addresses by hand or you
       can let Postfix do it for you (which is the default).  See the
       description of the mynetworks_style parameter for more information.

       If you specify the mynetworks list by hand, Postfix ignores the
       mynetworks_style setting.

       Specify a list of network addresses or network/netmask patterns,
       separated by commas and/or whitespace. Continue long lines by starting
       the next line with whitespace.

       The netmask specifies the number of bits in the network part of a host
       address.  You can also specify "/file/name" or "type:table" patterns.
       A "/file/name" pattern is replaced by its contents; a "type:table"
       lookup table is matched when a table entry matches a lookup string (the
       lookup result is ignored).

       The list is matched left to right, and the search stops on the first
       match.  Specify "!pattern" to exclude an address or network block from
       the list. The form "!/file/name" is supported only in Postfix version
       2.4 and later.

       Note: IP version 6 address information must be specified inside [] in
       the mynetworks value, and in files specified with "/file/name".  IP
       version 6 addresses contain the ":" character, and would otherwise be
       confused with a "type:table" pattern.

       Examples:

       mynetworks = 127.0.0.0/8 168.100.189.0/28
       mynetworks = !192.168.0.1, 192.168.0.0/28
       mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
       mynetworks = $config_directory/mynetworks
       mynetworks = hash:/etc/postfix/network_table

mynetworks_style (default: subnet)
       The method to generate the default value for the mynetworks parameter.
       This is the list of trusted networks for relay access control etc.

       o      Specify "mynetworks_style = host" when Postfix should "trust"
              only the local machine.

       o      Specify "mynetworks_style = subnet" when Postfix should "trust"
              SMTP clients in the same IP subnetworks as the local machine.
              On Linux, this works correctly only with interfaces specified
              with the "ifconfig" command.

       o      Specify "mynetworks_style = class" when Postfix should "trust"
              SMTP clients in the same IP class A/B/C networks as the local
              machine.  Don't do this with a dialup site - it would cause
              Postfix to "trust" your entire provider's network.  Instead,
              specify an explicit mynetworks list by hand, as described with
              the mynetworks configuration parameter.

myorigin (default: $myhostname)
       The domain name that locally-posted mail appears to come from, and that
       locally posted mail is delivered to. The default, $myhostname, is
       adequate for small sites.  If you run a domain with multiple machines,
       you should (1) change this to $mydomain and (2) set up a domain-wide
       alias database that aliases each user to userATthat.mailhost.

       Example:

       myorigin = $mydomain

nested_header_checks (default: $header_checks)
       Optional lookup tables for content inspection of non-MIME message
       headers in attached messages, as described in the header_checks(5)
       manual page.

       This feature is available in Postfix 2.0 and later.

newaliases_path (default: see postconf -d output)
       Sendmail compatibility feature that specifies the location of the
       newaliases(1) command. This command can be used to rebuild the local(8)
       aliases(5) database.

non_fqdn_reject_code (default: 504)
       The numerical Postfix SMTP server reply code when a client request is
       rejected by the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender
       or reject_non_fqdn_recipient restriction.

non_smtpd_milters (default: empty)
       A list of Milter (mail filter) applications for new mail that does not
       arrive via the Postfix smtpd(8) server. This includes local submission
       via the sendmail(1) command line, new mail that arrives via the Postfix
       qmqpd(8) server, and old mail that is re-injected into the queue with
       "postsuper -r".  See the MILTER_README document for details.

       This feature is available in Postfix 2.3 and later.

notify_classes (default: resource, software)
       The list of error classes that are reported to the postmaster. The
       default is to report only the most serious problems. The paranoid may
       wish to turn on the policy (UCE and mail relaying) and protocol error
       (broken mail software) reports.

       NOTE: postmaster notifications may contain confidential information
       such as SASL passwords or message content.  It is the system
       administrator's responsibility to treat such information with care.

       The error classes are:

       bounce (also implies 2bounce)
              Send the postmaster copies of the headers of bounced mail, and
              send transcripts of SMTP sessions when Postfix rejects mail. The
              notification is sent to the address specified with the
              bounce_notice_recipient configuration parameter (default:
              postmaster).

       2bounce
              Send undeliverable bounced mail to the postmaster. The
              notification is sent to the address specified with the
              2bounce_notice_recipient configuration parameter (default:
              postmaster).

       delay  Send the postmaster copies of the headers of delayed mail. The
              notification is sent to the address specified with the
              delay_notice_recipient configuration parameter (default:
              postmaster).

       policy Send the postmaster a transcript of the SMTP session when a
              client request was rejected because of (UCE) policy. The
              notification is sent to the address specified with the
              error_notice_recipient configuration parameter (default:
              postmaster).

       protocol
              Send the postmaster a transcript of the SMTP session in case of
              client or server protocol errors. The notification is sent to
              the address specified with the error_notice_recipient
              configuration parameter (default: postmaster).

       resource
              Inform the postmaster of mail not delivered due to resource
              problems.  The notification is sent to the address specified
              with the error_notice_recipient configuration parameter
              (default: postmaster).

       software
              Inform the postmaster of mail not delivered due to software
              problems.  The notification is sent to the address specified
              with the error_notice_recipient configuration parameter
              (default: postmaster).

       Examples:

       notify_classes = bounce, delay, policy, protocol, resource, software
       notify_classes = 2bounce, resource, software

owner_request_special (default: yes)
       Give special treatment to owner-listname and listname-request address
       localparts: don't split such addresses when the recipient_delimiter is
       set to "-".  This feature is useful for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)
       What Postfix features match subdomains of "domain.tld" automatically,
       instead of requiring an explicit ".domain.tld" pattern.  This is
       planned backwards compatibility:  eventually, all Postfix features are
       expected to require explicit ".domain.tld" style patterns when you
       really want to match subdomains.

permit_mx_backup_networks (default: empty)
       Restrict the use of the permit_mx_backup SMTP access feature to only
       domains whose primary MX hosts match the listed networks.  The
       parameter value syntax is the same as with the mynetworks parameter;
       note, however, that the default value is empty.

pickup_service_name (default: pickup)
       The name of the pickup(8) service. This service picks up local mail
       submissions from the Postfix maildrop queue.

       This feature is available in Postfix 2.0 and later.

plaintext_reject_code (default: 450)
       The numerical Postfix SMTP server response code when a request is
       rejected by the reject_plaintext_session restriction.

       This feature is available in Postfix 2.3 and later.

postmulti_control_commands (default: reload flush)
       The postfix(1) commands that the postmulti(1) instance manager treats
       as "control" commands, that operate on running instances. For these
       commands, disabled instances are skipped.

       This feature is available in Postfix 2.6 and later.

postmulti_start_commands (default: start)
       The postfix(1) commands that the postmulti(1) instance manager treats
       as "start" commands. For these commands, disabled instances are
       "checked" rather than "started", and failure to "start" a member
       instance of an instance group will abort the start-up of later
       instances.

       This feature is available in Postfix 2.6 and later.

postmulti_stop_commands (default: see postconf -d output)
       The postfix(1) commands that the postmulti(1) instance manager treats
       as "stop" commands. For these commands, disabled instances are skipped,
       and enabled instances are processed in reverse order.

       This feature is available in Postfix 2.6 and later.

postscreen_access_list (default: permit_mynetworks)
       Permanent white/blacklist for remote SMTP client IP addresses.
       postscreen(8) searches this list immediately after a remote SMTP client
       connects.  Specify a comma- or whitespace-separated list of commands
       (in upper or lower case) or lookup tables. The search stops upon the
       first command that fires for the client IP address.

        permit_mynetworks
              Whitelist the client and terminate the search if the client IP
              address matches $mynetworks.  Do not subject the client to any
              before/after 220 greeting tests.  Pass the connection
              immediately to a Postfix SMTP server process.

        type:table
              Query the specified lookup table. Each table lookup result is an
              access list, except that access lists inside a table cannot
              specify type:table entries.
              To discourage the use of hash, btree, etc. tables, there is no
              support for substring matching like smtpd(8). Use CIDR tables
              instead.

        permit
              Whitelist the client and terminate the search. Do not subject
              the client to any before/after 220 greeting tests. Pass the
              connection immediately to a Postfix SMTP server process.

        reject
              Blacklist the client and terminate the search. Subject the
              client to the action configured with the
              postscreen_blacklist_action configuration parameter.

        dunno
              All postscreen(8) access lists implicitly have this command at
              the end.
              When  dunno  is executed inside a lookup table, return from the
              lookup table and evaluate the next command.
              When  dunno  is executed outside a lookup table, terminate the
              search, and subject the client to the configured before/after
              220 greeting tests.

       Example:

       /etc/postfix/main.cf:
           postscreen_access_list = permit_mynetworks,
                 cidr:/etc/postfix/postscreen_access.cidr

       /etc/postfix/postscreen_access.cidr:
           # Rules are evaluated in the order as specified.
           # Blacklist 192.168.* except 192.168.0.1.
           192.168.0.1         dunno
           192.168.0.0/16      reject

       This feature is available in Postfix 2.8.

postscreen_bare_newline_action (default: ignore)
       The action that postscreen(8) takes when an SMTP client sends a bare
       newline character, that is, a newline not preceded by carriage return.
       Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to complete.
              Do not repeat this test before some the result from some other
              test expires.  This option is useful for testing and collecting
              statistics without blocking mail permanently.

       enforce
              Allow other tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient
              information.  Repeat this test the next time the client
              connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_enable (default: no)
       Enable "bare newline" SMTP protocol tests in the postscreen(8) server.
       These tests are expensive: a client must disconnect after it passes the
       test, before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from a
       successful "bare newline" SMTP protocol test. During this time, the
       client IP address is excluded from this test. The default is long
       because a client must disconnect after it passes the test, before it
       can talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_blacklist_action (default: ignore)
       The action that postscreen(8) takes when an SMTP client is permanently
       blacklisted with the postscreen_access_list parameter.  Specify one of
       the following:

       ignore (default)
              Ignore  this result. Allow other tests to complete.  Repeat this
              test the next time the client connects.  This option is useful
              for testing and collecting statistics without blocking mail.

       enforce
              Allow other tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient
              information.  Repeat this test the next time the client
              connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_cache_cleanup_interval (default: 12h)
       The amount of time between postscreen(8) cache cleanup runs.  Cache
       cleanup increases the load on the cache database and should therefore
       not be run frequently. This feature requires that the cache database
       supports the "delete" and "sequence" operators.  Specify a zero
       interval to disable cache cleanup.

       After each cache cleanup run, the postscreen(8) daemon logs the number
       of entries that were retained and dropped. A cleanup run is logged as
       "partial" when the daemon terminates early after "postfix reload",
       "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_cache_map (default: btree:$data_directory/postscreen_cache)
       Persistent storage for the postscreen(8) server decisions.

       This feature is available in Postfix 2.8.

postscreen_cache_retention_time (default: 7d)
       The amount of time that postscreen(8) will cache an expired temporary
       whitelist entry before it is removed. This prevents clients from being
       logged as "NEW" just because their cache entry expired an hour ago. It
       also prevents the cache from filling up with clients that passed some
       deep protocol test once and never came back.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_client_connection_count_limit (default:
$smtpd_client_connection_count_limit)
       How many simultaneous connections any client is allowed to have with
       the postscreen(8) daemon. By default, this limit is the same as with
       the Postfix SMTP server. Note that the triage process can take several
       seconds, with the time spent in postscreen_greet_wait delay, and with
       the time spent talking to the postscreen(8) built-in dummy SMTP
       protocol engine.

       This feature is available in Postfix 2.8.

postscreen_command_count_limit (default: 20)
       The limit on the total number of commands per SMTP session for
       postscreen(8)'s built-in SMTP protocol engine.  This SMTP engine defers
       or rejects all attempts to deliver mail, therefore there is no need to
       enforce separate limits on the number of junk commands and error
       commands.

       This feature is available in Postfix 2.8.

postscreen_command_filter (default: $smtpd_command_filter)
       A mechanism to transform commands from remote SMTP clients.  See
       smtpd_command_filter for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_command_time_limit (default: ${stress?10}${stress:300}s)
       The time limit to read an entire command line with postscreen(8)'s
       built-in SMTP protocol engine.

       This feature is available in Postfix 2.8.

postscreen_disable_vrfy_command (default: $disable_vrfy_command)
       Disable the SMTP VRFY command in the postscreen(8) daemon.  See
       disable_vrfy_command for details.

       This feature is available in Postfix 2.8.

postscreen_discard_ehlo_keyword_address_maps (default:
$smtpd_discard_ehlo_keyword_address_maps)
       Lookup tables, indexed by the remote SMTP client address, with case
       insensitive lists of EHLO keywords (pipelining, starttls, auth, etc.)
       that the postscreen(8) server will not send in the EHLO response to a
       remote SMTP client. See smtpd_discard_ehlo_keywords for details.  The
       table is not searched by hostname for robustness reasons.

       This feature is available in Postfix 2.8 and later.

postscreen_discard_ehlo_keywords (default: $smtpd_discard_ehlo_keywords)
       A case insensitive list of EHLO keywords (pipelining, starttls, auth,
       etc.) that the postscreen(8) server will not send in the EHLO response
       to a remote SMTP client. See smtpd_discard_ehlo_keywords for details.

       This feature is available in Postfix 2.8 and later.

postscreen_dnsbl_action (default: ignore)
       The action that postscreen(8) takes when an SMTP client's combined
       DNSBL score is equal to or greater than a threshold (as defined with
       the postscreen_dnsbl_sites and postscreen_dnsbl_threshold parameters).
       Specify one of the following:

       ignore (default)
              Ignore the failure of this test. Allow other tests to complete.
              Repeat this test the next time the client connects.  This option
              is useful for testing and collecting statistics without blocking
              mail.

       enforce
              Allow other tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient
              information.  Repeat this test the next time the client
              connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_reply_map (default: empty)
       A mapping from actual DNSBL domain name which includes a secret
       password, to the DNSBL domain name that postscreen will reply with when
       it rejects mail.  When no mapping is found, the actual DNSBL domain
       will be used.

       For maximal stability it is best to use a file that is read into memory
       such as pcre:, regexp: or texthash: (texthash: is similar to hash:,
       except a) there is no need to run postmap(1) before the file can be
       used, and b) texthash: does not detect changes after the file is read).

       Example:

       /etc/postfix/main.cf:
           postscreen_dnsbl_reply_map = texthash:/etc/postfix/dnsbl_reply

       /etc/postfix/dnsbl_reply:
          secret.zen.spamhaus.org   zen.spamhaus.org

       This feature is available in Postfix 2.8.

postscreen_dnsbl_sites (default: empty)
       Optional list of DNS white/blacklist domains, filters and weight
       factors. When the list is non-empty, the dnsblog(8) daemon will query
       these domains with the IP addresses of remote SMTP clients, and
       postscreen(8) will update an SMTP client's DNSBL score with each non-
       error reply.

       Caution: when postscreen rejects mail, it replies with the DNSBL domain
       name. Use the postscreen_dnsbl_reply_map feature to hide "password"
       information in DNSBL domain names.

       When a client's score is equal to or greater than the threshold
       specified with postscreen_dnsbl_threshold, postscreen(8) can drop the
       connection with the SMTP client.

       Specify a list of domain=filter*weight entries, separated by comma or
       whitespace.

       o      When no "=filter" is specified, postscreen(8) will use any non-
              error DNSBL reply.  Otherwise, postscreen(8) uses only DNSBL
              replies that match the filter. The filter has the form d.d.d.d,
              where each d is a number, or a pattern inside [] that contains
              one or more ";"-separated numbers or number..number ranges.

       o      When no "*weight" is specified, postscreen(8) increments the
              SMTP client's DNSBL score by 1.  Otherwise, the weight must be
              an integral number, and postscreen(8) adds the specified weight
              to the SMTP client's DNSBL score.  Specify a negative number for
              whitelisting.

       o      When one postscreen_dnsbl_sites entry produces multiple DNSBL
              responses, postscreen(8) applies the weight at most once.

       Examples:

       To use example.com as a high-confidence blocklist, and to block mail
       with example.net and example.org only when both agree:

       postscreen_dnsbl_threshold = 2
       postscreen_dnsbl_sites = example.com*2, example.net, example.org

       To filter only DNSBL replies containing 127.0.0.4:

       postscreen_dnsbl_sites = example.com=127.0.0.4

       This feature is available in Postfix 2.8.

postscreen_dnsbl_threshold (default: 1)
       The inclusive lower bound for blocking an SMTP client, based on its
       combined DNSBL score as defined with the postscreen_dnsbl_sites
       parameter.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_ttl (default: 1h)
       The amount of time that postscreen(8) will use the result from a
       successful DNS blocklist test. During this time, the client IP address
       is excluded from this test. The default is relatively short, because a
       good client can immediately talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory TLS: announce STARTTLS support to SMTP clients, and require
       that clients use TLS encryption.  See smtpd_postscreen_enforce_tls for
       details.

       This feature is available in Postfix 2.8 and later.  Preferably, use
       postscreen_tls_security_level instead.

postscreen_expansion_filter (default: see postconf -d output)
       List of characters that are permitted in postscreen_reject_footer
       attribute expansions.  See smtpd_expansion_filter for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_forbidden_commands (default: $smtpd_forbidden_commands)
       List of commands that the postscreen(8) server considers in violation
       of the SMTP protocol. See smtpd_forbidden_commands for syntax, and
       postscreen_non_smtp_command_action for possible actions.

       This feature is available in Postfix 2.8.

postscreen_greet_action (default: ignore)
       The action that postscreen(8) takes when an SMTP client speaks before
       its turn within the time specified with the postscreen_greet_wait
       parameter.  Specify one of the following:

       ignore (default)
              Ignore the failure of this test. Allow other tests to complete.
              Repeat this test the next time the client connects.  This option
              is useful for testing and collecting statistics without blocking
              mail.

       enforce
              Allow other tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient
              information.  Repeat this test the next time the client
              connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       In either case, postscreen(8) will not whitelist the SMTP client IP
       address.

       This feature is available in Postfix 2.8.

postscreen_greet_banner (default: $smtpd_banner)
       The text in the optional "220-text..." server response that
       postscreen(8) sends ahead of the real Postfix SMTP server's "220
       text..." response, in an attempt to confuse bad SMTP clients so that
       they speak before their turn (pre-greet).  Specify an empty value to
       disable this feature.

       This feature is available in Postfix 2.8.

postscreen_greet_ttl (default: 1d)
       The amount of time that postscreen(8) will use the result from a
       successful PREGREET test. During this time, the client IP address is
       excluded from this test. The default is relatively short, because a
       good client can immediately talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_greet_wait (default: ${stress?2}${stress:6}s)
       The amount of time that postscreen(8) will wait for an SMTP client to
       send a command before its turn, and for DNS blocklist lookup results to
       arrive (default: up to 2 seconds under stress, up to 6 seconds
       otherwise).

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_helo_required (default: $smtpd_helo_required)
       Require that a remote SMTP client sends HELO or EHLO before commencing
       a MAIL transaction.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_action (default: drop)
       The action that postscreen(8) takes when an SMTP client sends non-SMTP
       commands as specified with the postscreen_forbidden_commands parameter.
       Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to complete.
              Do not repeat this test before some the result from some other
              test expires.  This option is useful for testing and collecting
              statistics without blocking mail permanently.

       enforce
              Allow other tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient
              information.  Repeat this test the next time the client
              connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects. This action is the
              same as with the Postfix SMTP server's smtpd_forbidden_commands
              feature.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_enable (default: no)
       Enable "non-SMTP command" tests in the postscreen(8) server. These
       tests are expensive: a client must disconnect after it passes the test,
       before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from a
       successful "non_smtp_command" SMTP protocol test. During this time, the
       client IP address is excluded from this test. The default is long
       because a client must disconnect after it passes the test, before it
       can talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_pipelining_action (default: enforce)
       The action that postscreen(8) takes when an SMTP client sends multiple
       commands instead of sending one command and waiting for the server to
       respond.  Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to complete.
              Do not repeat this test before some the result from some other
              test expires.  This option is useful for testing and collecting
              statistics without blocking mail permanently.

       enforce
              Allow other tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient
              information.  Repeat this test the next time the client
              connects.

       drop   Drop the connection immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_pipelining_enable (default: no)
       Enable "pipelining" SMTP protocol tests in the postscreen(8) server.
       These tests are expensive: a good client must disconnect after it
       passes the test, before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_pipelining_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from a
       successful "pipelining" SMTP protocol test. During this time, the
       client IP address is excluded from this test. The default is long
       because a good client must disconnect after it passes the test, before
       it can talk to a real Postfix SMTP server.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_post_queue_limit (default: $default_process_limit)
       The number of clients that can be waiting for service from a real SMTP
       server process. When this queue is full, all clients will receive a 421
       reponse.

       This feature is available in Postfix 2.8.

postscreen_pre_queue_limit (default: $default_process_limit)
       The number of non-whitelisted clients that can be waiting for a
       decision whether they will receive service from a real SMTP server
       process. When this queue is full, all non-whitelisted clients will
       receive a 421 reponse.

       This feature is available in Postfix 2.8.

postscreen_reject_footer (default: $smtpd_reject_footer)
       Optional information that is appended after a 4XX or 5XX server
       response. See smtpd_reject_footer for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_tls_security_level (default: $smtpd_tls_security_level)
       The SMTP TLS security level for the postscreen(8) server; when a non-
       empty value is specified, this overrides the obsolete parameters
       postscreen_use_tls and postscreen_enforce_tls. See
       smtpd_tls_security_level for details.

       This feature is available in Postfix 2.8 and later.

postscreen_use_tls (default: $smtpd_use_tls)
       Opportunistic TLS: announce STARTTLS support to SMTP clients, but do
       not require that clients use TLS encryption.

       This feature is available in Postfix 2.8 and later.  Preferably, use
       postscreen_tls_security_level instead.

postscreen_watchdog_timeout (default: 10s)
       How much time a postscreen(8) process may take to respond to an SMTP
       client command or to perform a cache operation before it is terminated
       by a built-in watchdog timer.  This is a safety mechanism that prevents
       postscreen(8) from becoming non-responsive due to a bug in Postfix
       itself or in system software.  To avoid false alarms and unnecessary
       cache corruption this limit cannot be set under 10s.

       Specify a non-zero time value (an integral value plus an optional one-
       letter suffix that specifies the time unit).  Time units: s (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

prepend_delivered_header (default: command, file, forward)
       The message delivery contexts where the Postfix local(8) delivery agent
       prepends a Delivered-To:  message header with the address that the mail
       was delivered to. This information is used for mail delivery loop
       detection.

       By default, the Postfix local delivery agent prepends a Delivered-To:
       header when forwarding mail and when delivering to file (mailbox) and
       command. Turning off the Delivered-To: header when forwarding mail is
       not recommended.

       Specify zero or more of forward, file, or command.

       Example:

       prepend_delivered_header = forward

process_id (read-only)
       The process ID of a Postfix command or daemon process.

process_id_directory (default: pid)
       The location of Postfix PID files relative to $queue_directory.  This
       is a read-only parameter.

process_name (read-only)
       The process name of a Postfix command or daemon process.

propagate_unmatched_extensions (default: canonical, virtual)
       What address lookup tables copy an address extension from the lookup
       key to the lookup result.

       For example, with a virtual(5) mapping of "joe@example.com =&gt;
       joe.user@example.net", the address "joe+foo@example.com" would rewrite
       to "joe.user+foo@example.net".

       Specify zero or more of canonical, virtual, alias, forward, include or
       generic. These cause address extension propagation with canonical(5),
       virtual(5), and aliases(5) maps, with local(8) .forward and :include:
       file lookups, and with smtp(8) generic maps, respectively.

       Note: enabling this feature for types other than canonical and virtual
       is likely to cause problems when mail is forwarded to other sites,
       especially with mail that is sent to a mailing list exploder address.

       Examples:

       propagate_unmatched_extensions = canonical, virtual, alias,
               forward, include
       propagate_unmatched_extensions = canonical, virtual

proxy_interfaces (default: empty)
       The network interface addresses that this mail system receives mail on
       by way of a proxy or network address translation unit.

       This feature is available in Postfix 2.0 and later.

       You must specify your "outside" proxy/NAT addresses when your system is
       a backup MX host for other domains, otherwise mail delivery loops will
       happen when the primary MX host is down.

       Example:

       proxy_interfaces = 1.2.3.4

proxy_read_maps (default: see postconf -d output)
       The lookup tables that the proxymap(8) server is allowed to access for
       the read-only service.  Table references that don't begin with proxy:
       are ignored.

       This feature is available in Postfix 2.0 and later.

proxy_write_maps (default: see postconf -d output)
       The lookup tables that the proxymap(8) server is allowed to access for
       the read-write service. Postfix-owned local database files should be
       stored under the Postfix-owned data_directory.  Table references that
       don't begin with proxy: are ignored.

       This feature is available in Postfix 2.5 and later.

proxymap_service_name (default: proxymap)
       The name of the proxymap read-only table lookup service.  This service
       is normally implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

proxywrite_service_name (default: proxywrite)
       The name of the proxywrite read-write table lookup service.  This
       service is normally implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

qmgr_clog_warn_time (default: 300s)
       The minimal delay between warnings that a specific destination is
       clogging up the Postfix active queue. Specify 0 to disable.

       This feature is enabled with the helpful_warnings parameter.

       This feature is available in Postfix 2.0 and later.

qmgr_daemon_timeout (default: 1000s)
       How much time a Postfix queue manager process may take to handle a
       request before it is terminated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_fudge_factor (default: 100)
       Obsolete feature: the percentage of delivery resources that a busy mail
       system will use up for delivery of a large mailing  list message.

       This feature exists only in the oqmgr(8) old queue manager. The current
       queue manager solves the problem in a better way.

qmgr_ipc_timeout (default: 60s)
       The time limit for the queue manager to send or receive information
       over an internal communication channel.  The purpose is to break out of
       deadlock situations. If the time limit is exceeded the software either
       retries or aborts the operation.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_message_active_limit (default: 20000)
       The maximal number of messages in the active queue.

qmgr_message_recipient_limit (default: 20000)
       The maximal number of recipients held in memory by the Postfix queue
       manager, and the maximal size of the size of the short-term, in-memory
       "dead" destination status cache.

qmgr_message_recipient_minimum (default: 10)
       The minimal number of in-memory recipients for any message. This takes
       priority over any other in-memory recipient limits (i.e., the global
       qmgr_message_recipient_limit and the per transport _recipient_limit) if
       necessary. The minimum value allowed for this parameter is 1.

qmqpd_authorized_clients (default: empty)
       What clients are allowed to connect to the QMQP server port.

       By default, no client is allowed to use the service. This is because
       the QMQP server will relay mail to any destination.

       Specify a list of client patterns. A list pattern specifies a host
       name, a domain name, an internet address, or a network/mask pattern,
       where the mask specifies the number of bits in the network part.  When
       a pattern specifies a file name, its contents are substituted for the
       file name; when a pattern is a "type:table" table specification, table
       lookup is used instead.

       Patterns are separated by whitespace and/or commas. In order to reverse
       the result, precede a pattern with an exclamation point (!). The form
       "!/file/name" is supported only in Postfix version 2.4 and later.

       Example:

       qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

qmqpd_client_port_logging (default: no)
       Enable logging of the remote QMQP client port in addition to the
       hostname and IP address. The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

qmqpd_error_delay (default: 1s)
       How long the QMQP server will pause before sending a negative reply to
       the client. The purpose is to slow down confused or malicious clients.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

qmqpd_timeout (default: 300s)
       The time limit for sending or receiving information over the network.
       If a read or write operation blocks for more than $qmqpd_timeout
       seconds the QMQP server gives up and disconnects.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

queue_directory (default: see postconf -d output)
       The location of the Postfix top-level queue directory. This is the root
       directory of Postfix daemon processes that run chrooted.

queue_file_attribute_count_limit (default: 100)
       The maximal number of (name=value) attributes that may be stored in a
       Postfix queue file. The limit is enforced by the cleanup(8) server.

       This feature is available in Postfix 2.0 and later.

queue_minfree (default: 0)
       The minimal amount of free space in bytes in the queue file system that
       is needed to receive mail.  This is currently used by the SMTP server
       to decide if it will accept any mail at all.

       By default, the Postfix SMTP server rejects MAIL FROM commands when the
       amount of free space is less than 1.5*$message_size_limit (Postfix
       version 2.1 and later).  To specify a higher minimum free space limit,
       specify a queue_minfree value that is at least 1.5*$message_size_limit.

       With Postfix versions 2.0 and earlier, a queue_minfree value of zero
       means there is no minimum required amount of free space.

queue_run_delay (default: 300s)
       The time between deferred queue scans by the queue manager; prior to
       Postfix 2.4 the default value was 1000s.

       This parameter should be set less than or equal to
       $minimal_backoff_time. See also $maximal_backoff_time.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

queue_service_name (default: qmgr)
       The name of the qmgr(8) service. This service manages the Postfix queue
       and schedules delivery requests.

       This feature is available in Postfix 2.0 and later.

rbl_reply_maps (default: empty)
       Optional lookup tables with RBL response templates. The tables are
       indexed by the RBL domain name. By default, Postfix uses the default
       template as specified with the default_rbl_reply configuration
       parameter. See there for a discussion of the syntax of RBL reply
       templates.

       This feature is available in Postfix 2.0 and later.

readme_directory (default: see postconf -d output)
       The location of Postfix README files that describe how to build,
       configure or operate a specific Postfix subsystem or feature.

receive_override_options (default: empty)
       Enable or disable recipient validation, built-in content filtering, or
       address mapping. Typically, these are specified in master.cf as
       command-line arguments for the smtpd(8), qmqpd(8) or pickup(8) daemons.

       Specify zero or more of the following options.  The options override
       main.cf settings and are either implemented by smtpd(8), qmqpd(8), or
       pickup(8) themselves, or they are forwarded to the cleanup server.

       no_unknown_recipient_checks
              Do not try to reject unknown recipients (SMTP server only).
              This is typically specified AFTER an external content filter.

       no_address_mappings
              Disable canonical address mapping, virtual alias map expansion,
              address masquerading, and automatic BCC (blind carbon-copy)
              recipients. This is typically specified BEFORE an external
              content filter.

       no_header_body_checks
              Disable header/body_checks. This is typically specified AFTER an
              external content filter.

       no_milters
              Disable Milter (mail filter) applications. This is typically
              specified AFTER an external content filter.

       Note: when the "BEFORE content filter" receive_override_options setting
       is specified in the main.cf file, specify the "AFTER content filter"
       receive_override_options setting in master.cf (and vice versa).

       Examples:

       receive_override_options =
           no_unknown_recipient_checks, no_header_body_checks
       receive_override_options = no_address_mappings

       This feature is available in Postfix 2.1 and later.

recipient_bcc_maps (default: empty)
       Optional BCC (blind carbon-copy) address lookup tables, indexed by
       recipient address.  The BCC address (multiple results are not
       supported) is added when mail enters from outside of Postfix.

       This feature is available in Postfix 2.1 and later.

       The table search order is as follows:

       o      Look up the "user+extensionATdomain.tld" address including the
              optional address extension.

       o      Look up the "userATdomain.tld" address without the optional
              address extension.

       o      Look up the "user+extension" address local part when the
              recipient domain equals $myorigin, $mydestination,
              $inet_interfaces or $proxy_interfaces.

       o      Look up the "user" address local part when the recipient domain
              equals $myorigin, $mydestination, $inet_interfaces or
              $proxy_interfaces.

       o      Look up the "@domain.tld" part.

       Specify the types and names of databases to use.  After change, run
       "postmap /etc/postfix/recipient_bcc".

       Note: if mail to the BCC address bounces it will be returned to the
       sender.

       Note: automatic BCC recipients are produced only for new mail.  To
       avoid mailer loops, automatic BCC recipients are not generated after
       Postfix forwards mail internally, or after Postfix generates mail
       itself.

       Example:

       recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

recipient_canonical_classes (default: envelope_recipient, header_recipient)
       What addresses are subject to recipient_canonical_maps address mapping.
       By default, recipient_canonical_maps address mapping is applied to
       envelope recipient addresses, and to header recipient addresses.

       Specify one or more of: envelope_recipient, header_recipient

       This feature is available in Postfix 2.2 and later.

recipient_canonical_maps (default: empty)
       Optional address mapping lookup tables for envelope and header
       recipient addresses.  The table format and lookups are documented in
       canonical(5).

       Note: $recipient_canonical_maps is processed before $canonical_maps.

       Example:

       recipient_canonical_maps = hash:/etc/postfix/recipient_canonical

recipient_delimiter (default: empty)
       The separator between user names and address extensions (user+foo).
       See canonical(5), local(8), relocated(5) and virtual(5) for the effects
       this has on aliases, canonical, virtual, relocated and on .forward file
       lookups.  Basically, the software tries user+foo and .forward+foo
       before trying user and .forward.

       Example:

       recipient_delimiter = +

reject_code (default: 554)
       The numerical Postfix SMTP server response code when a remote SMTP
       client request is rejected by the "reject" restriction.

       Do not change this unless you have a complete understanding of RFC
       2821.

reject_tempfail_action (default: defer_if_permit)
       The Postfix SMTP server's action when a reject-type restriction fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP client request immediately. With the default "defer_if_permit"
       action, the Postfix SMTP server continues to look for opportunities to
       reject mail, and defers the client request only if it would otherwise
       be accepted.

       For finer control, see: unverified_recipient_tempfail_action,
       unverified_sender_tempfail_action, unknown_address_tempfail_action, and
       unknown_helo_hostname_tempfail_action.

       This feature is available in Postfix 2.6 and later.

relay_clientcerts (default: empty)
       List of tables with remote SMTP client-certificate fingerprints for
       which the Postfix SMTP server will allow access with the
       permit_tls_clientcerts feature.  The fingerprint digest algorithm is
       configurable via the smtpd_tls_fingerprint_digest parameter (hard-coded
       as md5 prior to Postfix version 2.5).

       Postfix lookup tables are in the form of (key, value) pairs.  Since we
       only need the key, the value can be chosen freely, e.g.  the name of
       the user or host: D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80
       lutzpc.at.home

       Example:

       relay_clientcerts = hash:/etc/postfix/relay_clientcerts

       For more fine-grained control, use check_ccert_access to select an
       appropriate access(5) policy for each client.  See
       RESTRICTION_CLASS_README.

       This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit (default:
$default_destination_concurrency_limit)
       The maximal number of parallel deliveries to the same destination via
       the relay message delivery transport. This limit is enforced by the
       queue manager. The message delivery transport name is the first field
       in the entry in the master.cf file.

       This feature is available in Postfix 2.0 and later.

relay_destination_recipient_limit (default:
$default_destination_recipient_limit)
       The maximal number of recipients per message for the relay message
       delivery transport. This limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of
       relay_destination_concurrency_limit from concurrency per domain into
       concurrency per recipient.

       This feature is available in Postfix 2.0 and later.

relay_domains (default: $mydestination)
       What destination domains (and subdomains thereof) this system will
       relay mail to. Subdomain matching is controlled with the
       parent_domain_matches_subdomains parameter. For details about how the
       relay_domains value is used, see the description of the
       permit_auth_destination and reject_unauth_destination SMTP recipient
       restrictions.

       Domains that match $relay_domains are delivered with the
       $relay_transport mail delivery transport. The SMTP server validates
       recipient addresses with $relay_recipient_maps and rejects non-existent
       recipients. See also the relay domains address class in the
       ADDRESS_CLASS_README file.

       Note: Postfix will not automatically forward mail for domains that list
       this system as their primary or backup MX host. See the
       permit_mx_backup restriction in the postconf(5) manual page.

       Specify a list of host or domain names, "/file/name" patterns or
       "type:table" lookup tables, separated by commas and/or whitespace.
       Continue long lines by starting the next line with whitespace. A
       "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table is matched when a (parent) domain appears as lookup key. Specify
       "!pattern" to exclude a domain from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

relay_domains_reject_code (default: 554)
       The numerical Postfix SMTP server response code when a client request
       is rejected by the reject_unauth_destination recipient restriction.

       Do not change this unless you have a complete understanding of RFC
       2821.

relay_recipient_maps (default: empty)
       Optional lookup tables with all valid addresses in the domains that
       match $relay_domains. Specify @domain as a wild-card for domains that
       have no valid recipient list, and become a source of backscatter mail:
       Postfix accepts spam for non-existent recipients and then floods
       innocent people with undeliverable mail.  Technically, tables listed
       with $relay_recipient_maps are used as lists: Postfix needs to know
       only if a lookup string is found or not, but it does not use the result
       from table lookup.

       If this parameter is non-empty, then the Postfix SMTP server will
       reject mail to unknown relay users. This feature is off by default.

       See also the relay domains address class in the ADDRESS_CLASS_README
       file.

       Example:

       relay_recipient_maps = hash:/etc/postfix/relay_recipients

       This feature is available in Postfix 2.0 and later.

relay_transport (default: relay)
       The default mail delivery transport and next-hop destination for remote
       delivery to domains listed with $relay_domains. In order of decreasing
       precedence, the nexthop destination is taken from $relay_transport,
       $sender_dependent_relayhost_maps, $relayhost, or from the recipient
       domain. This information can be overruled with the transport(5) table.

       Specify a string of the form transport:nexthop, where transport is the
       name of a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       See also the relay domains address class in the ADDRESS_CLASS_README
       file.

       This feature is available in Postfix 2.0 and later.

relayhost (default: empty)
       The next-hop destination of non-local mail; overrides non-local domains
       in recipient addresses. This information is overruled with
       relay_transport, sender_dependent_default_transport_maps,
       default_transport, sender_dependent_relayhost_maps and with the
       transport(5) table.

       On an intranet, specify the organizational domain name. If your
       internal DNS uses no MX records, specify the name of the intranet
       gateway host instead.

       In the case of SMTP, specify a domain name, hostname, hostname:port,
       [hostname]:port, [hostaddress] or [hostaddress]:port. The form
       [hostname] turns off MX lookups.

       If you're connected via UUCP, see the UUCP_README file for useful
       information.

       Examples:

       relayhost = $mydomain
       relayhost = [gateway.example.com]
       relayhost = uucphost
       relayhost = [an.ip.add.ress]

relocated_maps (default: empty)
       Optional lookup tables with new contact information for users or
       domains that no longer exist.  The table format and lookups are
       documented in relocated(5).

       If you use this feature, run "postmap /etc/postfix/relocated" to build
       the necessary DBM or DB file after change, then "postfix reload" to
       make the changes visible.

       Examples:

       relocated_maps = dbm:/etc/postfix/relocated
       relocated_maps = hash:/etc/postfix/relocated

remote_header_rewrite_domain (default: empty)
       Don't rewrite message headers from remote clients at all when this
       parameter is empty; otherwise, rewrite message headers and append the
       specified domain name to incomplete addresses.  The
       local_header_rewrite_clients parameter controls what clients Postfix
       considers local.

       Examples:

       The safe setting: append "domain.invalid" to incomplete header
       addresses from remote SMTP clients, so that those addresses cannot be
       confused with local addresses.

           remote_header_rewrite_domain = domain.invalid

       The default, purist, setting: don't rewrite headers from remote clients
       at all.

           remote_header_rewrite_domain =

require_home_directory (default: no)
       Require that a local(8) recipient's home directory exists before mail
       delivery is attempted. By default this test is disabled.  It can be
       useful for environments that import home directories to the mail server
       (IMPORTING HOME DIRECTORIES IS NOT RECOMMENDED).

reset_owner_alias (default: no)
       Reset the local(8) delivery agent's idea of the owner-alias attribute,
       when delivering mail to a child alias that does not have its own owner
       alias.

       This feature is available in Postfix 2.8 and later. With older Postfix
       releases, the behavior is as if this parameter is set to "yes".

       As documented in aliases(5), when an alias name has a companion alias
       named owner-name, delivery errors will be reported to the owner alias
       instead of the sender. This configuration is recommended for mailing
       lists.

       A less known property of the owner alias is that it also forces the
       local(8) delivery agent to write local and remote addresses from alias
       expansion to a new queue file, instead of attempting to deliver mail to
       local addresses as soon as they come out of alias expansion.

       Writing local addresses from alias expansion to a new queue file allows
       for robust handling of temporary delivery errors: errors with one local
       member have no effect on deliveries to other members of the list.  On
       the other hand, delivery to local addresses as soon as they come out of
       alias expansion is fragile: a temporary error with one local address
       from alias expansion will cause the entire alias to be expanded
       repeatedly until the error goes away, or until the message expires in
       the queue.  In that case, a problem with one list member results in
       multiple message deliveries to other list members.

       The default behavior of Postfix 2.8 and later is to keep the owner-
       alias attribute of the parent alias, when delivering mail to a child
       alias that does not have its own owner alias. Then, local addresses
       from that child alias will be written to a new queue file, and a
       temporary error with one local address will not affect delivery to
       other mailing list members.

       Unfortunately, older Postfix releases reset the owner-alias attribute
       when delivering mail to a child alias that does not have its own owner
       alias.  The local(8) delivery agent then attempts to deliver local
       addresses as soon as they come out of child alias expansion.  If
       delivery to any address from child alias expansion fails with a
       temporary error condition, the entire mailing list may be expanded
       repeatedly until the mail expires in the queue, resulting in multiple
       deliveries of the same message to mailing list members.

resolve_dequoted_address (default: yes)
       Resolve a recipient address safely instead of correctly, by looking
       inside quotes.

       By default, the Postfix address resolver does not quote the address
       localpart as per RFC 822, so that additional @ or % or !  operators
       remain visible. This behavior is safe but it is also technically
       incorrect.

       If you specify "resolve_dequoted_address = no", then the Postfix
       resolver will not know about additional @ etc. operators in the address
       localpart. This opens opportunities for obscure mail relay attacks with
       user@domain@domain addresses when Postfix provides backup MX service
       for Sendmail systems.

resolve_null_domain (default: no)
       Resolve an address that ends in the "@" null domain as if the local
       hostname were specified, instead of rejecting the address as invalid.

       This feature is available in Postfix 2.1 and later.  Earlier versions
       always resolve the null domain as the local hostname.

       The Postfix SMTP server uses this feature to reject mail from or to
       addresses that end in the "@" null domain, and from addresses that
       rewrite into a form that ends in the "@" null domain.

resolve_numeric_domain (default: no)
       Resolve "user@ipaddress" as "user@[ipaddress]", instead of rejecting
       the address as invalid.

       This feature is available in Postfix 2.3 and later.

rewrite_service_name (default: rewrite)
       The name of the address rewriting service. This service rewrites
       addresses to standard form and resolves them to a (delivery method,
       next-hop host, recipient) triple.

       This feature is available in Postfix 2.0 and later.

sample_directory (default: /etc/postfix)
       The name of the directory with example Postfix configuration files.
       Starting with Postfix 2.1, these files have been replaced with the
       postconf(5) manual page.

send_cyrus_sasl_authzid (default: no)
       When authenticating to a remote SMTP or LMTP server with the default
       setting "no", send no SASL authoriZation ID (authzid); send only the
       SASL authentiCation ID (authcid) plus the authcid's password.

       The non-default setting "yes" enables the behavior of older Postfix
       versions.  These always send a SASL authzid that is equal to the SASL
       authcid, but this causes inter-operability problems with some SMTP
       servers.

       This feature is available in Postfix 2.4.4 and later.

sender_based_routing (default: no)
       This parameter should not be used. It was replaced by
       sender_dependent_relayhost_maps in Postfix version 2.3.

sender_bcc_maps (default: empty)
       Optional BCC (blind carbon-copy) address lookup tables, indexed by
       sender address.  The BCC address (multiple results are not supported)
       is added when mail enters from outside of Postfix.

       This feature is available in Postfix 2.1 and later.

       The table search order is as follows:

       o      Look up the "user+extensionATdomain.tld" address including the
              optional address extension.

       o      Look up the "userATdomain.tld" address without the optional
              address extension.

       o      Look up the "user+extension" address local part when the sender
              domain equals $myorigin, $mydestination, $inet_interfaces or
              $proxy_interfaces.

       o      Look up the "user" address local part when the sender domain
              equals $myorigin, $mydestination, $inet_interfaces or
              $proxy_interfaces.

       o      Look up the "@domain.tld" part.

       Specify the types and names of databases to use.  After change, run
       "postmap /etc/postfix/sender_bcc".

       Note: if mail to the BCC address bounces it will be returned to the
       sender.

       Note: automatic BCC recipients are produced only for new mail.  To
       avoid mailer loops, automatic BCC recipients are not generated after
       Postfix forwards mail internally, or after Postfix generates mail
       itself.

       Example:

       sender_bcc_maps = hash:/etc/postfix/sender_bcc

sender_canonical_classes (default: envelope_sender, header_sender)
       What addresses are subject to sender_canonical_maps address mapping.
       By default, sender_canonical_maps address mapping is applied to
       envelope sender addresses, and to header sender addresses.

       Specify one or more of: envelope_sender, header_sender

       This feature is available in Postfix 2.2 and later.

sender_canonical_maps (default: empty)
       Optional address mapping lookup tables for envelope and header sender
       addresses.  The table format and lookups are documented in
       canonical(5).

       Example: you want to rewrite the SENDER address "userATugly.domain" to
       "userATpretty.domain", while still being able to send mail to the
       RECIPIENT address "userATugly.domain".

       Note: $sender_canonical_maps is processed before $canonical_maps.

       Example:

       sender_canonical_maps = hash:/etc/postfix/sender_canonical

sender_dependent_default_transport_maps (default: empty)
       A sender-dependent override for the global default_transport parameter
       setting. The tables are searched by the envelope sender address and
       @domain. A lookup result of DUNNO terminates the search without
       overriding the global default_transport parameter setting.  This
       information is overruled with the transport(5) table.

       Note: this overrides default_transport, not transport_maps, and
       therefore the expected syntax is that of default_transport, not the
       syntax of transport_maps.  Specifically, this does not support the
       transport_maps syntax for null transport, null nexthop, or null email
       addresses.

       For safety reasons, this feature does not allow $number substitutions
       in regular expression maps.

       This feature is available in Postfix 2.7 and later.

sender_dependent_relayhost_maps (default: empty)
       A sender-dependent override for the global relayhost parameter setting.
       The tables are searched by the envelope sender address and @domain. A
       lookup result of DUNNO terminates the search without overriding the
       global relayhost parameter setting (Postfix 2.6 and later). This
       information is overruled with relay_transport,
       sender_dependent_default_transport_maps, default_transport and with the
       transport(5) table.

       For safety reasons, this feature does not allow $number substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

sendmail_path (default: see postconf -d output)
       A Sendmail compatibility feature that specifies the location of the
       Postfix sendmail(1) command. This command can be used to submit mail
       into the Postfix queue.

service_throttle_time (default: 60s)
       How long the Postfix master(8) waits before forking a server that
       appears to be malfunctioning.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

setgid_group (default: postdrop)
       The group ownership of set-gid Postfix commands and of group-writable
       Postfix directories. When this parameter value is changed you need to
       re-run "postfix set-permissions" (with Postfix version 2.0 and earlier:
       "/etc/postfix/post-install set-permissions".

show_user_unknown_table_name (default: yes)
       Display the name of the recipient table in the "User unknown"
       responses.  The extra detail makes trouble shooting easier but also
       reveals information that is nobody elses business.

       This feature is available in Postfix 2.0 and later.

showq_service_name (default: showq)
       The name of the showq(8) service. This service produces mail queue
       status reports.

       This feature is available in Postfix 2.0 and later.

smtp_address_preference (default: ipv6)
       The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client
       will try first, when a destination has IPv6 and IPv4 addresses with
       equal MX preference. This feature has no effect unless the
       inet_protocols setting enables both IPv4 and IPv6.

       This feature is available in Postfix 2.8 and later.

smtp_always_send_ehlo (default: yes)
       Always send EHLO at the start of an SMTP session.

       With "smtp_always_send_ehlo = no", Postfix sends EHLO only when the
       word "ESMTP" appears in the server greeting banner (example: 220
       spike.porcupine.org ESMTP Postfix).

smtp_bind_address (default: empty)
       An optional numerical network address that the Postfix SMTP client
       should bind to when making an IPv4 connection.

       This can be specified in the main.cf file for all SMTP clients, or it
       can be specified in the master.cf file for a specific client, for
       example:

           /etc/postfix/master.cf:
               smtp ... smtp -o smtp_bind_address=11.22.33.44

       Note 1: when inet_interfaces specifies no more than one IPv4 address,
       and that address is a non-loopback address, it is automatically used as
       the smtp_bind_address.  This supports virtual IP hosting, but can be a
       problem on multi-homed firewalls. See the inet_interfaces documentation
       for more detail.

       Note 2: address information may be enclosed inside [], but this form is
       not required here.

smtp_bind_address6 (default: empty)
       An optional numerical network address that the Postfix SMTP client
       should bind to when making an IPv6 connection.

       This feature is available in Postfix 2.2 and later.

       This can be specified in the main.cf file for all SMTP clients, or it
       can be specified in the master.cf file for a specific client, for
       example:

           /etc/postfix/master.cf:
               smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

       Note 1: when inet_interfaces specifies no more than one IPv6 address,
       and that address is a non-loopback address, it is automatically used as
       the smtp_bind_address6.  This supports virtual IP hosting, but can be a
       problem on multi-homed firewalls. See the inet_interfaces documentation
       for more detail.

       Note 2: address information may be enclosed inside [], but this form is
       not recommended here.

smtp_body_checks (default: empty)
       Restricted body_checks(5) tables for the Postfix SMTP client.  These
       tables are searched while mail is being delivered.  Actions that change
       the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_cname_overrides_servername (default: version dependent)
       Allow DNS CNAME records to override the servername that the Postfix
       SMTP client uses for logging, SASL password lookup, TLS policy
       decisions, or TLS certificate verification. The value "no" hardens
       Postfix smtp_tls_per_site hostname-based policies against false
       hostname information in DNS CNAME records, and makes SASL password file
       lookups more predictable. This is the default setting as of Postfix
       2.3.

       This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)
       The SMTP client time limit for completing a TCP connection, or zero
       (use the operating system built-in time limit).

       When no connection can be made within the deadline, the Postfix SMTP
       client tries the next address on the mail exchanger list. Specify 0 to
       disable the time limit (i.e. use whatever timeout is implemented by the
       operating system).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_connection_cache_destinations (default: empty)
       Permanently enable SMTP connection caching for the specified
       destinations.  With SMTP connection caching, a connection is not closed
       immediately after completion of a mail transaction.  Instead, the
       connection is kept open for up to $smtp_connection_cache_time_limit
       seconds.  This allows connections to be reused for other deliveries,
       and can improve mail delivery performance.

       Specify a comma or white space separated list of destinations or
       pseudo-destinations:

       o      if mail is sent without a relay host: a domain name (the right-
              hand side of an email address, without the [] around a numeric
              IP address),

       o      if mail is sent via a relay host: a relay host name (without []
              or non-default TCP port), as specified in main.cf or in the
              transport map,

       o      if mail is sent via a UNIX-domain socket: a pathname (without
              the unix: prefix),

       o      a /file/name with domain names and/or relay host names as
              defined above,

       o      a "type:table" with domain names and/or relay host names on the
              left-hand side.  The right-hand side result from "type:table"
              lookups is ignored.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_on_demand (default: yes)
       Temporarily enable SMTP connection caching while a destination has a
       high volume of mail in the active queue.  With SMTP connection caching,
       a connection is not closed immediately after completion of a mail
       transaction.  Instead, the connection is kept open for up to
       $smtp_connection_cache_time_limit seconds.  This allows connections to
       be reused for other deliveries, and can improve mail delivery
       performance.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_reuse_limit (default: 10)
       When SMTP connection caching is enabled, the number of times that an
       SMTP session may be reused before it is closed.

       This feature is available in Postfix 2.2. In Postfix 2.3 it is replaced
       by $smtp_connection_reuse_time_limit.

smtp_connection_cache_time_limit (default: 2s)
       When SMTP connection caching is enabled, the amount of time that an
       unused SMTP client socket is kept open before it is closed.  Do not
       specify larger values without permission from the remote sites.

       This feature is available in Postfix 2.2 and later.

smtp_connection_reuse_time_limit (default: 300s)
       The amount of time during which Postfix will use an SMTP connection
       repeatedly.  The timer starts when the connection is initiated (i.e. it
       includes the connect, greeting and helo latency, in addition to the
       latencies of subsequent mail delivery transactions).

       This feature addresses a performance stability problem with remote SMTP
       servers. This problem is not specific to Postfix: it can happen when
       any MTA sends large amounts of SMTP email to a site that has multiple
       MX hosts.

       The problem starts when one of a set of MX hosts becomes slower than
       the rest.  Even though SMTP clients connect to fast and slow MX hosts
       with equal probability, the slow MX host ends up with more simultaneous
       inbound connections than the faster MX hosts, because the slow MX host
       needs more time to serve each client request.

       The slow MX host becomes a connection attractor.  If one MX host
       becomes N times slower than the rest, it dominates mail delivery
       latency unless there are more than N fast MX hosts to counter the
       effect. And if the number of MX hosts is smaller than N, the mail
       delivery latency becomes effectively that of the slowest MX host
       divided by the total number of MX hosts.

       The solution uses connection caching in a way that differs from Postfix
       version 2.2.  By limiting the amount of time during which a connection
       can be used repeatedly (instead of limiting the number of deliveries
       over that connection), Postfix not only restores fairness in the
       distribution of simultaneous connections across a set of MX hosts, it
       also favors deliveries over connections that perform well, which is
       exactly what we want.

       The default reuse time limit, 300s, is comparable to the various smtp
       transaction timeouts which are fair estimates of maximum excess latency
       for a slow delivery.  Note that hosts may accept thousands of messages
       over a single connection within the default connection reuse time
       limit. This number is much larger than the default Postfix version 2.2
       limit of 10 messages per cached connection. It may prove necessary to
       lower the limit to avoid interoperability issues with MTAs that exhibit
       bugs when many messages are delivered via a single connection.  A lower
       reuse time limit risks losing the benefit of connection reuse when the
       average connection and mail delivery latency exceeds the reuse time
       limit.

       This feature is available in Postfix 2.3 and later.

smtp_data_done_timeout (default: 600s)
       The SMTP client time limit for sending the SMTP ".", and for receiving
       the server response.

       When no response is received within the deadline, a warning is logged
       that the mail may be delivered multiple times.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_data_init_timeout (default: 120s)
       The SMTP client time limit for sending the SMTP DATA command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_data_xfer_timeout (default: 180s)
       The SMTP client time limit for sending the SMTP message content.  When
       the connection makes no progress for more than $smtp_data_xfer_timeout
       seconds the Postfix SMTP client terminates the transfer.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_defer_if_no_mx_address_found (default: no)
       Defer mail delivery when no MX record resolves to an IP address.

       The default (no) is to return the mail as undeliverable. With older
       Postfix versions the default was to keep trying to deliver the mail
       until someone fixed the MX record or until the mail was too old.

       Note: Postfix always ignores MX records with equal or worse preference
       than the local MTA itself.

       This feature is available in Postfix 2.1 and later.

smtp_destination_concurrency_limit (default:
$default_destination_concurrency_limit)
       The maximal number of parallel deliveries to the same destination via
       the smtp message delivery transport. This limit is enforced by the
       queue manager. The message delivery transport name is the first field
       in the entry in the master.cf file.

smtp_destination_recipient_limit (default:
$default_destination_recipient_limit)
       The maximal number of recipients per message for the smtp message
       delivery transport. This limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of
       smtp_destination_concurrency_limit from concurrency per domain into
       concurrency per recipient.

smtp_discard_ehlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with case
       insensitive lists of EHLO keywords (pipelining, starttls, auth, etc.)
       that the Postfix SMTP client will ignore in the EHLO response from a
       remote SMTP server. See smtp_discard_ehlo_keywords for details. The
       table is not indexed by hostname for consistency with
       smtpd_discard_ehlo_keyword_address_maps.

       This feature is available in Postfix 2.2 and later.

smtp_discard_ehlo_keywords (default: empty)
       A case insensitive list of EHLO keywords (pipelining, starttls, auth,
       etc.) that the Postfix SMTP client will ignore in the EHLO response
       from a remote SMTP server.

       This feature is available in Postfix 2.2 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

       o      Use the smtp_discard_ehlo_keyword_address_maps feature to
              discard EHLO keywords selectively.

smtp_dns_resolver_options (default: empty)
       DNS Resolver options for the Postfix SMTP client.  Specify zero or more
       of the following options, separated by comma or whitespace.  Option
       names are case-sensitive. Some options refer to domain names that are
       specified in the file /etc/resolv.conf or equivalent.

       res_defnames
              Append the current domain name to single-component names (those
              that do not contain a "." character). This can produce incorrect
              results, and is the hard-coded behavior prior to Postfix 2.8.

       res_dnsrch
              Search for host names in the current domain and in parent
              domains. This can produce incorrect results and is therefore not
              recommended.

       This feature is available in Postfix 2.8 and later.

smtp_enforce_tls (default: no)
       Enforcement mode: require that remote SMTP servers use TLS encryption,
       and never send mail in the clear.  This also requires that the remote
       SMTP server hostname matches the information in the remote server
       certificate, and that the remote SMTP server certificate was issued by
       a CA that is trusted by the Postfix SMTP client. If the certificate
       doesn't verify or the hostname doesn't match, delivery is deferred and
       mail stays in the queue.

       The server hostname is matched against all names provided as dNSNames
       in the SubjectAlternativeName.  If no dNSNames are specified, the
       CommonName is checked.  The behavior may be changed with the
       smtp_tls_enforce_peername option.

       This option is useful only if you are definitely sure that you will
       only connect to servers that support RFC 2487 _and_ that provide valid
       server certificates.  Typical use is for clients that send all their
       email to a dedicated mailhub.

       This feature is available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_security_level instead.

smtp_fallback_relay (default: $fallback_relay)
       Optional list of relay hosts for SMTP destinations that can't be found
       or that are unreachable. With Postfix 2.2 and earlier this parameter is
       called fallback_relay.

       By default, mail is returned to the sender when a destination is not
       found, and delivery is deferred when a destination is unreachable.

       The fallback relays must be SMTP destinations. Specify a domain, host,
       host:port, [host]:port, [address] or [address]:port; the form [host]
       turns off MX lookups.  If you specify multiple SMTP destinations,
       Postfix will try them in the specified order.

       To prevent mailer loops between MX hosts and fall-back hosts, Postfix
       version 2.2 and later will not use the fallback relays for destinations
       that it is MX host for (assuming DNS lookup is turned on).

smtp_generic_maps (default: empty)
       Optional lookup tables that perform address rewriting in the SMTP
       client, typically to transform a locally valid address into a globally
       valid address when sending mail across the Internet.  This is needed
       when the local machine does not have its own Internet domain name, but
       uses something like localdomain.local instead.

       The table format and lookups are documented in generic(5); examples are
       shown in the ADDRESS_REWRITING_README and STANDARD_CONFIGURATION_README
       documents.

       This feature is available in Postfix 2.2 and later.

smtp_header_checks (default: empty)
       Restricted header_checks(5) tables for the Postfix SMTP client.  These
       tables are searched while mail is being delivered.  Actions that change
       the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_helo_name (default: $myhostname)
       The hostname to send in the SMTP EHLO or HELO command.

       The default value is the machine hostname.  Specify a hostname or
       [ip.add.re.ss].

       This information can be specified in the main.cf file for all SMTP
       clients, or it can be specified in the master.cf file for a specific
       client, for example:

           /etc/postfix/master.cf:
               mysmtp ... smtp -o smtp_helo_name=foo.bar.com

       This feature is available in Postfix 2.0 and later.

smtp_helo_timeout (default: 300s)
       The SMTP client time limit for sending the HELO or EHLO command, and
       for receiving the initial server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_host_lookup (default: dns)
       What mechanisms the Postfix SMTP client uses to look up a host's IP
       address.  This parameter is ignored when DNS lookups are disabled (see:
       disable_dns_lookups).

       Specify one of the following:

       dns    Hosts can be found in the DNS (preferred).

       native Use the native naming service only (nsswitch.conf, or equivalent
              mechanism).

       dns, native
              Use the native service for hosts not found in the DNS.

       This feature is available in Postfix 2.1 and later.

smtp_line_length_limit (default: 990)
       The maximal length of message header and body lines that Postfix will
       send via SMTP.  Longer lines are broken by inserting "<CR><LF><SPACE>".
       This minimizes the damage to MIME formatted mail.

       By default, the line length is limited to 990 characters, because some
       server implementations cannot receive mail with long lines.

smtp_mail_timeout (default: 300s)
       The SMTP client time limit for sending the MAIL FROM command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_mime_header_checks (default: empty)
       Restricted mime_header_checks(5) tables for the Postfix SMTP client.
       These tables are searched while mail is being delivered.  Actions that
       change the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_mx_address_limit (default: 5)
       The maximal number of MX (mail exchanger) IP addresses that can result
       from mail exchanger lookups, or zero (no limit). Prior to Postfix
       version 2.3, this limit was disabled by default.

       This feature is available in Postfix 2.1 and later.

smtp_mx_session_limit (default: 2)
       The maximal number of SMTP sessions per delivery request before giving
       up or delivering to a fall-back relay host, or zero (no limit). This
       restriction ignores sessions that fail to complete the SMTP initial
       handshake (Postfix version 2.2 and earlier) or that fail to complete
       the EHLO and TLS handshake (Postfix version 2.3 and later).

       This feature is available in Postfix 2.1 and later.

smtp_nested_header_checks (default: empty)
       Restricted nested_header_checks(5) tables for the Postfix SMTP client.
       These tables are searched while mail is being delivered.  Actions that
       change the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_never_send_ehlo (default: no)
       Never send EHLO at the start of an SMTP session. See also the
       smtp_always_send_ehlo parameter.

smtp_pix_workaround_delay_time (default: 10s)
       How long the Postfix SMTP client pauses before sending ".<CR><LF>" in
       order to work around the PIX firewall "<CR><LF>.<CR><LF>" bug.

       Choosing a too short time makes this workaround ineffective when
       sending large messages over slow network connections.

smtp_pix_workaround_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with per-
       destination workarounds for CISCO PIX firewall bugs.  The table is not
       indexed by hostname for consistency with
       smtp_discard_ehlo_keyword_address_maps.

       This feature is available in Postfix 2.4 and later.

smtp_pix_workaround_threshold_time (default: 500s)
       How long a message must be queued before the Postfix SMTP client turns
       on the PIX firewall "<CR><LF>.<CR><LF>" bug workaround for delivery
       through firewalls with "smtp fixup" mode turned on.

       By default, the workaround is turned off for mail that is queued for
       less than 500 seconds. In other words, the workaround is normally
       turned off for the first delivery attempt.

       Specify 0 to enable the PIX firewall "<CR><LF>.<CR><LF>" bug workaround
       upon the first delivery attempt.

smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)
       A list that specifies zero or more workarounds for CISCO PIX firewall
       bugs. These workarounds are implemented by the Postfix SMTP client.
       Workaround names are separated by comma or space, and are case
       insensitive.  This parameter setting can be overruled with per-
       destination smtp_pix_workaround_maps settings.

       delay_dotcrlf
              Insert a delay before sending ".<CR><LF>" after the end of the
              message content.  The delay is subject to the
              smtp_pix_workaround_delay_time and
              smtp_pix_workaround_threshold_time parameter settings.

       disable_esmtp
              Disable all extended SMTP commands: send HELO instead of EHLO.

       This feature is available in Postfix 2.4 and later. The default
       settings are backwards compatible with earlier Postfix versions.

smtp_quit_timeout (default: 300s)
       The SMTP client time limit for sending the QUIT command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_quote_rfc821_envelope (default: yes)
       Quote addresses in SMTP MAIL FROM and RCPT TO commands as required by
       RFC 2821. This includes putting quotes around an address localpart that
       ends in ".".

       The default is to comply with RFC 2821. If you have to send mail to a
       broken SMTP server, configure a special SMTP client in master.cf:

           /etc/postfix/master.cf:
               broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

       and route mail for the destination in question to the "broken-smtp"
       message delivery with a transport(5) table.

       This feature is available in Postfix 2.1 and later.

smtp_randomize_addresses (default: yes)
       Randomize the order of equal-preference MX host addresses.  This is a
       performance feature of the Postfix SMTP client.

smtp_rcpt_timeout (default: 300s)
       The SMTP client time limit for sending the SMTP RCPT TO command, and
       for receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_reply_filter (default: empty)
       A mechanism to transform replies from remote SMTP servers one line at a
       time.  This is a last-resort tool to work around server replies that
       break inter-operability with the Postfix SMTP client.  Other uses
       involve fault injection to test Postfix's handling of invalid
       responses.

       Notes:

       o      In the case of a multi-line reply, the Postfix SMTP client uses
              the final reply line's numerical SMTP reply code and enhanced
              status code.

       o      The numerical SMTP reply code (XYZ) takes precedence over the
              enhanced status code (X.Y.Z).  When the enhanced status code
              initial digit differs from the SMTP reply code initial digit, or
              when no enhanced status code is present, the Postfix SMTP client
              uses a generic enhanced status code (X.0.0) instead.

       Specify the name of a "type:table" lookup table. The search string is a
       single SMTP reply line as received from the remote SMTP server, except
       that the trailing <CR><LF> are removed.

       Examples:

       /etc/postfix/main.cf:
           smtp_reply_filter = pcre:/etc/postfix/reply_filter

       /etc/postfix/reply_filter:
           # Transform garbage into "250-filler..." so that it looks like
           # one line from a multi-line reply. It does not matter what we
           # substitute here as long it has the right syntax.  The Postfix
           # SMTP client will use the final line's numerical SMTP reply
           # code and enhanced status code.
           !/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage

       This feature is available in Postfix 2.7.

smtp_rset_timeout (default: 20s)
       The SMTP client time limit for sending the RSET command, and for
       receiving the server response. The SMTP client sends RSET in order to
       finish a recipient address probe, or to verify that a cached session is
       still usable.

       This feature is available in Postfix 2.1 and later.

smtp_sasl_auth_cache_name (default: empty)
       An optional table to prevent repeated SASL authentication failures with
       the same remote SMTP server hostname, username and password. Each table
       (key, value) pair contains a server name, a username and password, and
       the full server response. This information is stored when a remote SMTP
       server rejects an authentication attempt with a 535 reply code.  As
       long as the smtp_sasl_password_maps information does no change, and as
       long as the smtp_sasl_auth_cache_name information does not expire (see
       smtp_sasl_auth_cache_time) the Postfix SMTP client avoids SASL
       authentication attempts with the same server, username and password,
       and instead bounces or defers mail as controlled with the
       smtp_sasl_auth_soft_bounce configuration parameter.

       Use a per-destination delivery concurrency of 1 (for example,
       "smtp_destination_concurrency_limit = 1",
       "relay_destination_concurrency_limit = 1", etc.), otherwise multiple
       delivery agents may experience a login failure at the same time.

       The table must be accessed via the proxywrite service, i.e. the map
       name must start with "proxy:". The table should be stored under the
       directory specified with the data_directory parameter.

       This feature uses cryptographic hashing to protect plain-text
       passwords, and requires that Postfix is compiled with TLS support.

       Example:

       smtp_sasl_auth_cache_name = proxy:btree:/var/db/postfix/sasl_auth_cache

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_cache_time (default: 90d)
       The maximal age of an smtp_sasl_auth_cache_name entry before it is
       removed.

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix SMTP client.  By default, the
       Postfix SMTP client uses no authentication.

       Example:

       smtp_sasl_auth_enable = yes

smtp_sasl_auth_soft_bounce (default: yes)
       When a remote SMTP server rejects a SASL authentication request with a
       535 reply code, defer mail delivery instead of returning mail as
       undeliverable. The latter behavior was hard-coded prior to Postfix
       version 2.5.

       Note: the setting "yes" overrides the global soft_bounce parameter, but
       the setting "no" does not.

       Example:

       # Default as of Postfix 2.5
       smtp_sasl_auth_soft_bounce = yes
       # The old hard-coded default
       smtp_sasl_auth_soft_bounce = no

       This feature is available in Postfix 2.5 and later.

smtp_sasl_mechanism_filter (default: empty)
       If non-empty, a Postfix SMTP client filter for the remote SMTP server's
       list of offered SASL mechanisms.  Different client and server
       implementations may support different mechanism lists. By default, the
       Postfix SMTP client will use the intersection of the two.
       smtp_sasl_mechanism_filter further restricts what server mechanisms the
       client will take into consideration.

       Specify mechanism names, "/file/name" patterns or "type:table" lookup
       tables. The right-hand side result from "type:table" lookups is
       ignored. Specify "!pattern" to exclude a mechanism name from the list.
       The form "!/file/name" is supported only in Postfix version 2.4 and
       later.

       This feature is available in Postfix 2.2 and later.

       Examples:

       smtp_sasl_mechanism_filter = plain, login
       smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
       smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

smtp_sasl_password_maps (default: empty)
       Optional SMTP client lookup tables with one username:password entry per
       remote hostname or domain, or sender address when sender-dependent
       authentication is enabled.  If no username:password entry is found,
       then the Postfix SMTP client will not attempt to authenticate to the
       remote host.

       The Postfix SMTP client opens the lookup table before going to chroot
       jail, so you can leave the password file in /etc/postfix.

smtp_sasl_path (default: empty)
       Implementation-specific information that the Postfix SMTP client passes
       through to the SASL plug-in implementation that is selected with
       smtp_sasl_type.  Typically this specifies the name of a configuration
       file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

smtp_sasl_security_options (default: noplaintext, noanonymous)
       Postfix SMTP client SASL security options; as of Postfix 2.3 the list
       of available features depends on the SASL client implementation that is
       selected with smtp_sasl_type.

       The following security features are defined for the cyrus client SASL
       implementation:

       Specify zero or more of the following:

       noplaintext
              Disallow methods that use plaintext passwords.

       noactive
              Disallow methods subject to active (non-dictionary) attack.

       nodictionary
              Disallow methods subject to passive (dictionary) attack.

       noanonymous
              Disallow methods that allow anonymous authentication.

       mutual_auth
              Only allow methods that provide mutual authentication (not
              available with SASL version 1).

       Example:

       smtp_sasl_security_options = noplaintext

smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)
       The SASL authentication security options that the Postfix SMTP client
       uses for TLS encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtp_sasl_tls_verified_security_options (default:
$smtp_sasl_tls_security_options)
       The SASL authentication security options that the Postfix SMTP client
       uses for TLS encrypted SMTP sessions with a verified server
       certificate.

       When mail is sent to the public MX host for the recipient's domain,
       server certificates are by default optional, and delivery proceeds even
       if certificate verification fails. For delivery via a submission
       service that requires SASL authentication, it may be appropriate to
       send plaintext passwords only when the connection to the server is
       strongly encrypted and the server identity is verified.

       The smtp_sasl_tls_verified_security_options parameter makes it possible
       to only enable plaintext mechanisms when a secure connection to the
       server is available. Submission servers subject to this policy must
       either have verifiable certificates or offer suitable non-plaintext
       SASL mechanisms.

       This feature is available in Postfix 2.6 and later.

smtp_sasl_type (default: cyrus)
       The SASL plug-in type that the Postfix SMTP client should use for
       authentication.  The available types are listed with the "postconf -A"
       command.

       This feature is available in Postfix 2.3 and later.

smtp_send_xforward_command (default: no)
       Send the non-standard XFORWARD command when the Postfix SMTP server
       EHLO response announces XFORWARD support.

       This allows an "smtp" delivery agent, used for injecting mail into a
       content filter, to forward the name, address, protocol and HELO name of
       the original client to the content filter and downstream queuing SMTP
       server. This can produce more useful logging than localhost[127.0.0.1]
       etc.

       This feature is available in Postfix 2.1 and later.

smtp_sender_dependent_authentication (default: no)
       Enable sender-dependent authentication in the Postfix SMTP client; this
       is available only with SASL authentication, and disables SMTP
       connection caching to ensure that mail from different senders will use
       the appropriate credentials.

       This feature is available in Postfix 2.3 and later.

smtp_skip_4xx_greeting (default: yes)
       Skip SMTP servers that greet with a 4XX status code (go away, try again
       later).

       By default, Postfix moves on the next mail exchanger. Specify
       "smtp_skip_4xx_greeting = no" if Postfix should defer delivery
       immediately.

       This feature is available in Postfix 2.0 and earlier.  Later Postfix
       versions always skip SMTP servers that greet with a 4XX status code.

smtp_skip_5xx_greeting (default: yes)
       Skip SMTP servers that greet with a 5XX status code (go away, do not
       try again later).

       By default, the Postfix SMTP client moves on the next mail exchanger.
       Specify "smtp_skip_5xx_greeting = no" if Postfix should bounce the mail
       immediately. The default setting is incorrect, but it is what a lot of
       people expect to happen.

smtp_skip_quit_response (default: yes)
       Do not wait for the response to the SMTP QUIT command.

smtp_starttls_timeout (default: 300s)
       Time limit for Postfix SMTP client write and read operations during TLS
       startup and shutdown handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtp_tls_CAfile (default: empty)
       A file containing CA certificates of root CAs trusted to sign either
       remote SMTP server certificates or intermediate CA certificates.  These
       are loaded into memory before the smtp(8) client enters the chroot
       jail. If the number of trusted roots is large, consider using
       smtp_tls_CApath instead, but note that the latter directory must be
       present in the chroot jail if the smtp(8) client is chrooted. This file
       may also be used to augment the client certificate trust chain, but it
       is best to include all the required certificates directly in
       $smtp_tls_cert_file.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_CApath (default: empty)
       Directory with PEM format certificate authority certificates that the
       Postfix SMTP client uses to verify a remote SMTP server certificate.
       Don't forget to create the necessary "hash" links with, for example,
       "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".

       To use this option in chroot mode, this directory (or a copy) must be
       inside the chroot jail.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtp_tls_block_early_mail_reply (default: no)
       Try to detect a mail hijacking attack based on a TLS protocol
       vulnerability (CVE-2009-3555), where an attacker prepends malicious
       HELO, MAIL, RCPT, DATA commands to a Postfix SMTP client TLS session.
       The attack would succeed with non-Postfix SMTP servers that reply to
       the malicious HELO, MAIL, RCPT, DATA commands after negotiating the
       Postfix SMTP client TLS session.

       This feature is available in Postfix 2.7.

smtp_tls_cert_file (default: empty)
       File with the Postfix SMTP client RSA certificate in PEM format.  This
       file may also contain the Postfix SMTP client private RSA key, and
       these may be the same as the Postfix SMTP server RSA certificate and
       key file.

       Do not configure client certificates unless you must present client TLS
       certificates to one or more servers. Client certificates are not
       usually needed, and can cause problems in configurations that work well
       without them. The recommended setting is to let the defaults stand:

           smtp_tls_cert_file =
           smtp_tls_key_file =
           smtp_tls_dcert_file =
           smtp_tls_dkey_file =
           smtp_tls_eccert_file =
           smtp_tls_eckey_file =

       The best way to use the default settings is to comment out the above
       parameters in main.cf if present.

       To enable remote SMTP servers to verify the Postfix SMTP client
       certificate, the issuing CA certificates must be made available to the
       server. You should include the required certificates in the client
       certificate file, the client certificate first, then the issuing CA(s)
       (bottom-up order).

       Example: the certificate for "client.example.com" was issued by
       "intermediate CA" which itself has a certificate issued by "root CA".
       Create the client.pem file with "cat client_cert.pem
       intermediate_CA.pem root_CA.pem > client.pem".

       If you also want to verify remote SMTP server certificates issued by
       these CAs, you can add the CA certificates to the smtp_tls_CAfile, in
       which case it is not necessary to have them in the smtp_tls_cert_file,
       smtp_tls_dcert_file or smtp_tls_eccert_file.

       A certificate supplied here must be usable as an SSL client certificate
       and hence pass the "openssl verify -purpose sslclient ..." test.

       Example:

       smtp_tls_cert_file = /etc/postfix/client.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_cipherlist (default: empty)
       Obsolete Postfix < 2.3 control for the Postfix SMTP client TLS cipher
       list. As this feature applies to all TLS security levels, it is easy to
       create inter-operability problems by choosing a non-default cipher
       list. Do not use a non-default TLS cipher list on hosts that deliver
       email to the public Internet: you will be unable to send email to
       servers that only support the ciphers you exclude. Using a restricted
       cipher list may be more appropriate for an internal MTA, where one can
       exert some control over the TLS software and settings of the peer
       servers.

       Note: do not use "" quotes around the parameter value.

       This feature is available in Postfix version 2.2. It is not used with
       Postfix 2.3 and later; use smtp_tls_mandatory_ciphers instead.

smtp_tls_ciphers (default: export)
       The minimum TLS cipher grade that the Postfix SMTP client will use with
       opportunistic TLS encryption. Cipher types listed in
       smtp_tls_exclude_ciphers are excluded from the base definition of the
       selected cipher grade. The default value "export" ensures maximum
       inter-operability. Because encryption is optional, stronger controls
       are not appropriate, and this setting SHOULD NOT be changed unless the
       change is essential.

       When TLS is mandatory the cipher grade is chosen via the
       smtp_tls_mandatory_ciphers configuration parameter, see there for
       syntax details. See smtp_tls_policy_maps for information on how to
       configure ciphers on a per-destination basis.

       Example:
       smtp_tls_ciphers = export

       This feature is available in Postfix 2.6 and later. With earlier
       Postfix releases only the smtp_tls_mandatory_ciphers parameter is
       implemented, and opportunistic TLS always uses "export" or better (i.e.
       all) ciphers.

smtp_tls_dcert_file (default: empty)
       File with the Postfix SMTP client DSA certificate in PEM format.  This
       file may also contain the Postfix SMTP client private DSA key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_dcert_file = /etc/postfix/client-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_dkey_file (default: $smtp_tls_dcert_file)
       File with the Postfix SMTP client DSA private key in PEM format.  This
       file may be combined with the Postfix SMTP client DSA certificate file
       specified with $smtp_tls_dcert_file.

       The private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtp_tls_eccert_file (default: empty)
       File with the Postfix SMTP client ECDSA certificate in PEM format.
       This file may also contain the Postfix SMTP client ECDSA private key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_eccert_file = /etc/postfix/ecdsa-ccert.pem

       This feature is available in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_eckey_file (default: $smtp_tls_eccert_file)
       File with the Postfix SMTP client ECDSA private key in PEM format.
       This file may be combined with the Postfix SMTP client ECDSA
       certificate file specified with $smtp_tls_eccert_file.

       The private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_enforce_peername (default: yes)
       With mandatory TLS encryption, require that the remote SMTP server
       hostname matches the information in the remote SMTP server certificate.
       As of RFC 2487 the requirements for hostname checking for MTA clients
       are not specified.

       This option can be set to "no" to disable strict peer name checking.
       This setting has no effect on sessions that are controlled via the
       smtp_tls_per_site table.

       Disabling the hostname verification can make sense in closed
       environment where special CAs are created.  If not used carefully, this
       option opens the danger of a "man-in-the-middle" attack (the CommonName
       of this attacker will be logged).

       This feature is available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_security_level instead.

smtp_tls_exclude_ciphers (default: empty)
       List of ciphers or cipher types to exclude from the Postfix SMTP client
       cipher list at all TLS security levels. This is not an OpenSSL
       cipherlist, it is a simple list separated by whitespace and/or commas.
       The elements are a single cipher, or one or more "+" separated cipher
       properties, in which case only ciphers matching all the properties are
       excluded.

       Examples (some of these will cause problems):

           smtp_tls_exclude_ciphers = aNULL
           smtp_tls_exclude_ciphers = MD5, DES
           smtp_tls_exclude_ciphers = DES+MD5
           smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
           smtp_tls_exclude_ciphers = kEDH+aRSA

       The first setting, disables anonymous ciphers. The next setting
       disables ciphers that use the MD5 digest algorithm or the (single) DES
       encryption algorithm. The next setting disables ciphers that use MD5
       and DES together.  The next setting disables the two ciphers
       "AES256-SHA" and "DES-CBC3-MD5". The last setting disables ciphers that
       use "EDH" key exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtp_tls_fingerprint_cert_match (default: empty)
       List of acceptable remote SMTP server certificate fingerprints for the
       "fingerprint" TLS security level (smtp_tls_security_level =
       fingerprint). At this security level, certificate authorities are not
       used, and certificate expiration times are ignored. Instead, server
       certificates are verified directly via their "fingerprint". The
       fingerprint is a message digest of the server certificate. The digest
       algorithm is selected via the smtp_tls_fingerprint_digest parameter.

       When an smtp_tls_policy_maps table entry specifies the "fingerprint"
       security level, any "match" attributes in that entry specify the list
       of valid fingerprints for the corresponding destination. Multiple
       fingerprints can be combined with a "|" delimiter in a single match
       attribute, or multiple match attributes can be employed.

       Example: Certificate fingerprint verification with internal mailhub.
       Two matching fingerprints are listed. The relayhost may be multiple
       physical hosts behind a load-balancer, each with its own private/public
       key and self-signed certificate. Alternatively, a single relayhost may
       be in the process of switching from one set of private/public keys to
       another, and both keys are trusted just prior to the transition.

           relayhost = [mailhub.example.com]
           smtp_tls_security_level = fingerprint
           smtp_tls_fingerprint_digest = md5
           smtp_tls_fingerprint_cert_match =
               3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
               EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       Example: Certificate fingerprint verification with selected
       destinations.  As in the example above, we show two matching
       fingerprints:

           /etc/postfix/main.cf:
               smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
               smtp_tls_fingerprint_digest = md5

           /etc/postfix/tls_policy:
               example.com    fingerprint
                   match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
                   match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.5 and later.

smtp_tls_fingerprint_digest (default: md5)
       The message digest algorithm used to construct remote SMTP server
       certificate fingerprints. At the "fingerprint" TLS security level
       (smtp_tls_security_level = fingerprint), the server certificate is
       verified by directly matching its fingerprint. The fingerprint is the
       message digest of the server certificate using the selected algorithm.
       With a digest algorithm resistant to "second pre-image" attacks, it is
       not feasible to create a new public key and a matching certificate that
       has the same fingerprint.

       The default algorithm is md5; this is consistent with the backwards
       compatible setting of the digest used to verify client certificates in
       the SMTP server.

       The best practice algorithm is now sha1. Recent advances in hash
       function cryptanalysis have led to md5 being deprecated in favor of
       sha1.  However, as long as there are no known "second pre-image"
       attacks against md5, its use in this context can still be considered
       safe.

       While additional digest algorithms are often available with OpenSSL's
       libcrypto, only those used by libssl in SSL cipher suites are available
       to Postfix. For now this means just md5 or sha1.

       To find the fingerprint of a specific certificate file, with a specific
       digest algorithm, run:

           $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The text to the right of "=" sign is the desired fingerprint.  For
       example:

           $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
           SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       This feature is available in Postfix 2.5 and later.

smtp_tls_key_file (default: $smtp_tls_cert_file)
       File with the Postfix SMTP client RSA private key in PEM format.  This
       file may be combined with the Postfix SMTP client RSA certificate file
       specified with $smtp_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       Example:

       smtp_tls_key_file = $smtp_tls_cert_file

       This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)
       Enable additional Postfix SMTP client logging of TLS activity.  Each
       logging level also includes the information that is logged at a lower
       logging level.


              0 Disable logging of TLS activity.


              1 Log TLS handshake and certificate information.


              2 Log levels during TLS negotiation.


              3 Log hexadecimal and ASCII dump of TLS negotiation process.


              4 Log hexadecimal and ASCII dump of complete transmission after
              STARTTLS.

       Use "smtp_tls_loglevel = 3" only in case of problems. Use of loglevel 4
       is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtp_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP client will use with
       mandatory TLS encryption.  The default value "medium" is suitable for
       most destinations with which you may want to enforce TLS, and is beyond
       the reach of today's cryptanalytic methods. See smtp_tls_policy_maps
       for information on how to configure ciphers on a per-destination basis.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or better OpenSSL ciphers.  This is the
              default for opportunistic encryption. It is not recommended for
              mandatory encryption unless you must enforce TLS with "crippled"
              peers. The underlying cipherlist is specified via the
              tls_export_cipherlist configuration parameter, which you are
              strongly encouraged to not change.

       low    Enable "LOW" grade or better OpenSSL ciphers.  This setting is
              only appropriate for internal mail servers.  The underlying
              cipherlist is specified via the tls_low_cipherlist configuration
              parameter, which you are strongly encouraged to not change.

       medium Enable "MEDIUM" grade or better OpenSSL ciphers.  The underlying
              cipherlist is specified via the tls_medium_cipherlist
              configuration parameter, which you are strongly encouraged to
              not change.

       high   Enable only "HIGH" grade OpenSSL ciphers.  This setting may be
              appropriate when all mandatory TLS destinations (e.g. when all
              mail is routed to a suitably capable relayhost) support at least
              one "HIGH" grade cipher. The underlying cipherlist is specified
              via the tls_high_cipherlist configuration parameter, which you
              are strongly encouraged to not change.

       null   Enable only the "NULL" OpenSSL ciphers, these provide
              authentication without encryption.  This setting is only
              appropriate in the rare case that all servers are prepared to
              use NULL ciphers (not normally enabled in TLS servers). A
              plausible use-case is an LMTP server listening on a UNIX-domain
              socket that is configured to support "NULL" ciphers. The
              underlying cipherlist is specified via the tls_null_cipherlist
              configuration parameter, which you are strongly encouraged to
              not change.

       The underlying cipherlists for grades other than "null" include
       anonymous ciphers, but these are automatically filtered out if the
       Postfix SMTP client is configured to verify server certificates.  You
       are very unlikely to need to take any steps to exclude anonymous
       ciphers, they are excluded automatically as necessary.  If you must
       exclude anonymous ciphers at the "may" or "encrypt" security levels,
       when the Postfix SMTP client does not need or use peer certificates,
       set "smtp_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers
       only when TLS is enforced, set "smtp_tls_mandatory_exclude_ciphers =
       aNULL".

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_exclude_ciphers (default: empty)
       Additional list of ciphers or cipher types to exclude from the SMTP
       client cipher list at mandatory TLS security levels. This list works in
       addition to the exclusions listed with smtp_tls_exclude_ciphers (see
       there for syntax details).

       Starting with Postfix 2.6, the mandatory cipher exclusions can be
       specified on a per-destination basis via the TLS policy "exclude"
       attribute. See smtp_tls_policy_maps for notes and examples.

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: !SSLv2)
       List of SSL/TLS protocols that the Postfix SMTP client will use with
       mandatory TLS encryption.  In main.cf the values are separated by
       whitespace, commas or colons. In the policy table "protocols" attribute
       (see smtp_tls_policy_maps) the only valid separator is colon. An empty
       value means allow all protocols. The valid protocol names, (see
       \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". If an older Postfix version is linked against OpenSSL 1.0.1
       or later, these, or any other new protocol versions, are
       unconditionally enabled.

       With Postfix >= 2.5 the parameter syntax is expanded to support
       protocol exclusions. One can now explicitly exclude SSLv2 by setting
       "smtp_tls_mandatory_protocols = !SSLv2". To exclude both SSLv2 and
       SSLv3 set "smtp_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing the
       protocols to include, rather than protocols to exclude, is supported,
       but not recommended. The exclusion form more closely matches the
       behaviour when the OpenSSL library is newer than Postfix.

       Since SSL version 2 has known protocol weaknesses and is now
       deprecated, the default setting excludes "SSLv2".  This means that by
       default, SSL version 2 will not be used at the "encrypt" security level
       and higher.

       See the documentation of the smtp_tls_policy_maps parameter and
       TLS_README for more information about security levels.

       Example:

       # Preferred form with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Alternative form.
       smtp_tls_mandatory_protocols = TLSv1

       This feature is available in Postfix 2.3 and later.

smtp_tls_note_starttls_offer (default: no)
       Log the hostname of a remote SMTP server that offers STARTTLS, when TLS
       is not already enabled for that server.

       The logfile record looks like:

       postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]

       This feature is available in Postfix 2.2 and later.

smtp_tls_per_site (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS usage policy by
       next-hop destination and by remote SMTP server hostname.  When both
       lookups succeed, the more specific per-site policy (NONE, MUST, etc)
       overrides the less specific one (MAY), and the more secure per-site
       policy (MUST, etc) overrides the less secure one (NONE).  With Postfix
       2.3 and later smtp_tls_per_site is strongly discouraged: use
       smtp_tls_policy_maps instead.

       Use of the bare hostname as the per-site table lookup key is
       discouraged. Always use the full destination nexthop (enclosed in []
       with a possible ":port" suffix). A recipient domain or MX-enabled
       transport next-hop with no port suffix may look like a bare hostname,
       but is still a suitable destination.

       Specify a next-hop destination or server hostname on the left-hand
       side; no wildcards are allowed. The next-hop destination is either the
       recipient domain, or the destination specified with a transport(5)
       table, the relayhost parameter, or the relay_transport parameter.  On
       the right hand side specify one of the following keywords:

       NONE   Don't use TLS at all. This overrides a less specific MAY lookup
              result from the alternate host or next-hop lookup key, and
              overrides the global smtp_use_tls, smtp_enforce_tls, and
              smtp_tls_enforce_peername settings.

       MAY    Try to use TLS if the server announces support, otherwise use
              the unencrypted connection. This has less precedence than a more
              specific result (including NONE) from the alternate host or
              next-hop lookup key, and has less precedence than the more
              specific global "smtp_enforce_tls = yes" or
              "smtp_tls_enforce_peername = yes".

       MUST_NOPEERMATCH
              Require TLS encryption, but do not require that the remote SMTP
              server hostname matches the information in the remote SMTP
              server certificate, or that the server certificate was issued by
              a trusted CA. This overrides a less secure NONE or a less
              specific MAY lookup result from the alternate host or next-hop
              lookup key, and overrides the global smtp_use_tls,
              smtp_enforce_tls and smtp_tls_enforce_peername settings.

       MUST   Require TLS encryption, require that the remote SMTP server
              hostname matches the information in the remote SMTP server
              certificate, and require that the remote SMTP server certificate
              was issued by a trusted CA. This overrides a less secure NONE
              and MUST_NOPEERMATCH or a less specific MAY lookup result from
              the alternate host or next-hop lookup key, and overrides the
              global smtp_use_tls, smtp_enforce_tls and
              smtp_tls_enforce_peername settings.

       The above keywords correspond to the "none", "may", "encrypt" and
       "verify" security levels for the new smtp_tls_security_level parameter
       introduced in Postfix 2.3. Starting with Postfix 2.3, and independently
       of how the policy is specified, the smtp_tls_mandatory_ciphers and
       smtp_tls_mandatory_protocols parameters apply when TLS encryption is
       mandatory. Connections for which encryption is optional typically
       enable all "export" grade and better ciphers (see smtp_tls_ciphers and
       smtp_tls_protocols).

       As long as no secure DNS lookup mechanism is available, false hostnames
       in MX or CNAME responses can change the server hostname that Postfix
       uses for TLS policy lookup and server certificate verification. Even
       with a perfect match between the server hostname and the server
       certificate, there is no guarantee that Postfix is connected to the
       right server.  See TLS_README (Closing a DNS loophole with obsolete
       per-site TLS policies) for a possible work-around.

       This feature is available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_policy_maps instead.

smtp_tls_policy_maps (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS security policy
       by next-hop destination; when a non-empty value is specified, this
       overrides the obsolete smtp_tls_per_site parameter.  See TLS_README for
       a more detailed discussion of TLS security levels.

       The TLS policy table is indexed by the full next-hop destination, which
       is either the recipient domain, or the verbatim next-hop specified in
       the transport table, $local_transport, $virtual_transport,
       $relay_transport or $default_transport. This includes any enclosing
       square brackets and any non-default destination server port suffix. The
       LMTP socket type prefix (inet: or unix:) is not included in the lookup
       key.

       Only the next-hop domain, or $myhostname with LMTP over UNIX-domain
       sockets, is used as the nexthop name for certificate verification. The
       port and any enclosing square brackets are used in the table lookup
       key, but are not used for server name verification.

       When the lookup key is a domain name without enclosing square brackets
       or any :port suffix (typically the recipient domain), and the full
       domain is not found in the table, just as with the transport(5) table,
       the parent domain starting with a leading "." is matched recursively.
       This allows one to specify a security policy for a recipient domain and
       all its sub-domains.

       The lookup result is a security level, followed by an optional list of
       whitespace and/or comma separated name=value attributes that override
       related main.cf settings. The TLS security levels in order of
       increasing security are:

       none   No TLS. No additional attributes are supported at this level.

       may    Opportunistic TLS. Since sending in the clear is acceptable,
              demanding stronger than default TLS security merely reduces
              inter-operability. The optional "ciphers", "exclude" and
              "protocols" attributes (available for opportunistic TLS with
              Postfix >= 2.6) override the "smtp_tls_ciphers",
              "smtp_tls_exclude_ciphers" and "smtp_tls_protocols"
              configuration parameters. When opportunistic TLS handshakes
              fail, Postfix retries the connection with TLS disabled.  This
              allows mail delivery to sites with non-interoperable TLS
              implementations.

       encrypt
              Mandatory TLS encryption. At this level and higher, the optional
              "protocols" attribute overrides the main.cf
              smtp_tls_mandatory_protocols parameter, the optional "ciphers"
              attribute overrides the main.cf smtp_tls_mandatory_ciphers
              parameter, and the optional "exclude" attribute (Postfix >= 2.6)
              overrides the main.cf smtp_tls_mandatory_exclude_ciphers
              parameter. In the policy table, multiple protocols or excluded
              ciphers must be separated by colons, as attribute values may not
              contain whitespace or commas.

       fingerprint
              Certificate fingerprint verification. Available with Postfix 2.5
              and later. At this security level, there are no trusted
              certificate authorities. The certificate trust chain, expiration
              date, ... are not checked. Instead, the optional match
              attribute, or else the main.cf smtp_tls_fingerprint_cert_match
              parameter, lists the valid "fingerprints" of the server
              certificate. The digest algorithm used to calculate the
              fingerprint is selected by the smtp_tls_fingerprint_digest
              parameter. Multiple fingerprints can be combined with a "|"
              delimiter in a single match attribute, or multiple match
              attributes can be employed. The ":" character is not used as a
              delimiter as it occurs between each pair of fingerprint
              (hexadecimal) digits.

       verify Mandatory TLS verification.  At this security level, DNS MX
              lookups are trusted to be secure enough, and the name verified
              in the server certificate is usually obtained indirectly via
              unauthenticated DNS MX lookups.  The optional "match" attribute
              overrides the main.cf smtp_tls_verify_cert_match parameter. In
              the policy table, multiple match patterns and strategies must be
              separated by colons.  In practice explicit control over matching
              is more common with the "secure" policy, described below.

       secure Secure-channel TLS. At this security level, DNS MX lookups,
              though potentially used to determine the candidate next-hop
              gateway IP addresses, are not trusted to be secure enough for
              TLS peername verification. Instead, the default name verified in
              the server certificate is obtained directly from the next-hop,
              or is explicitly specified via the optional match attribute
              which overrides the main.cf smtp_tls_secure_cert_match
              parameter. In the policy table, multiple match patterns and
              strategies must be separated by colons.  The match attribute is
              most useful when multiple domains are supported by common
              server, the policy entries for additional domains specify
              matching rules for the primary domain certificate. While
              transport table overrides routing the secondary domains to the
              primary nexthop also allow secure verification, they risk
              delivery to the wrong destination when domains change hands or
              are re-assigned to new gateways. With the "match" attribute
              approach, routing is not perturbed, and mail is deferred if
              verification of a new MX host fails.

       Example:

       /etc/postfix/main.cf:
           smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
           # Postfix 2.5 and later
           smtp_tls_fingerprint_digest = md5

       /etc/postfix/tls_policy:
           example.edu                 none
           example.mil                 may
           example.gov                 encrypt protocols=TLSv1
           example.com                 verify ciphers=high
           example.net                 secure
           .example.net                secure match=.example.net:example.net
           [mail.example.org]:587      secure match=nexthop
           # Postfix 2.5 and later
           [thumb.example.org]          fingerprint
                match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
            match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1

       Note: The hostname strategy if listed in a non-default setting of
       smtp_tls_secure_cert_match or in the match attribute in the policy
       table can render the secure level vulnerable to DNS forgery. Do not use
       the hostname strategy for secure-channel configurations in environments
       where DNS security is not assured.

       This feature is available in Postfix 2.3 and later.

smtp_tls_protocols (default: !SSLv2)
       List of TLS protocols that the Postfix SMTP client will exclude or
       include with opportunistic TLS encryption. Starting with Postfix 2.6,
       the Postfix SMTP client will by default not use the obsolete SSLv2
       protocol.

       In main.cf the values are separated by whitespace, commas or colons. In
       the policy table (see smtp_tls_policy_maps) the only valid separator is
       colon. An empty value means allow all protocols. The valid protocol
       names, (see \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". If an older Postfix version is linked against OpenSSL 1.0.1
       or later, these, or any other new protocol versions, are
       unconditionally enabled.

       To include a protocol list its name, to exclude it, prefix the name
       with a "!" character. To exclude SSLv2 even for opportunistic TLS set
       "smtp_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
       "smtp_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the protocols
       to include, rather than protocols to exclude, is supported, but not
       recommended.  The exclusion form more closely matches the behaviour
       when the OpenSSL library is newer than Postfix.

       Example:
       # TLSv1 only!
       smtp_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtp_tls_scert_verifydepth (default: 9)
       The verification depth for remote SMTP server certificates. A depth of
       1 is sufficient if the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for
       compatibility with earlier Postfix behavior. Prior to Postfix 2.5, the
       default value was 5, but the limit was not actually enforced. If you
       have set this to a lower non-default value, certificates with longer
       trust chains may now fail to verify. Certificate chains with 1 or 2 CAs
       are common, deeper chains are more rare and any number between 5 and 9
       should suffice in practice. You can choose a lower number if, for
       example, you trust certificates directly signed by an issuing CA but
       not any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtp_tls_secure_cert_match (default: nexthop, dot-nexthop)
       The server certificate peername verification method for the "secure"
       TLS security level. In a "secure" TLS policy table
       ($smtp_tls_policy_maps) entry the optional "match" attribute overrides
       this main.cf setting.

       This parameter specifies one or more patterns or strategies separated
       by commas, whitespace or colons.  In the policy table the only valid
       separator is the colon character.

       For a description of the pattern and strategy syntax see the
       smtp_tls_verify_cert_match parameter. The "hostname" strategy should be
       avoided in this context, as in the absence of a secure global DNS,
       using the results of MX lookups in certificate verification is not
       immune to active (man-in-the-middle) attacks on DNS.

       Sample main.cf setting:

           smtp_tls_secure_cert_match = nexthop

       Sample policy table override:

           example.net     secure match=example.com:.example.com
           .example.net    secure match=example.com:.example.com

       This feature is available in Postfix 2.3 and later.

smtp_tls_security_level (default: empty)
       The default SMTP TLS security level for the Postfix SMTP client; when a
       non-empty value is specified, this overrides the obsolete parameters
       smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername.

       Specify one of the following security levels:

       none   TLS will not be used unless enabled for specific destinations
              via smtp_tls_policy_maps.

       may    Opportunistic TLS. Use TLS if this is supported by the remote
              SMTP server, otherwise use plaintext. Since sending in the clear
              is acceptable, demanding stronger than default TLS security
              merely reduces inter-operability.  The "smtp_tls_ciphers" and
              "smtp_tls_protocols" (Postfix >= 2.6) configuration parameters
              provide control over the protocols and cipher grade used with
              opportunistic TLS.  With earlier releases the opportunistic TLS
              cipher grade is always "export" and no protocols are disabled.
              When TLS handshakes fail, the connection is retried with TLS
              disabled.  This allows mail delivery to sites with non-
              interoperable TLS implementations.

       encrypt
              Mandatory TLS encryption. Since a minimum level of security is
              intended, it is reasonable to be specific about sufficiently
              secure protocol versions and ciphers. At this security level and
              higher, the main.cf parameters smtp_tls_mandatory_protocols and
              smtp_tls_mandatory_ciphers specify the TLS protocols and minimum
              cipher grade which the administrator considers secure enough for
              mandatory encrypted sessions. This security level is not an
              appropriate default for systems delivering mail to the Internet.

       fingerprint
              Certificate fingerprint verification. Available with Postfix 2.5
              and later. At this security level, there are no trusted
              certificate authorities. The certificate trust chain, expiration
              date, ... are not checked. Instead, the
              smtp_tls_fingerprint_cert_match parameter lists the valid
              "fingerprints" of the server certificate. The digest algorithm
              used to calculate the fingerprint is selected by the
              smtp_tls_fingerprint_digest parameter.

       verify Mandatory TLS verification. At this security level, DNS MX
              lookups are trusted to be secure enough, and the name verified
              in the server certificate is usually obtained indirectly via
              unauthenticated DNS MX lookups. The smtp_tls_verify_cert_match
              parameter controls how the server name is verified. In practice
              explicit control over matching is more common at the "secure"
              level, described below. This security level is not an
              appropriate default for systems delivering mail to the Internet.

       secure Secure-channel TLS.  At this security level, DNS MX lookups,
              though potentially used to determine the candidate next-hop
              gateway IP addresses, are not trusted to be secure enough for
              TLS peername verification. Instead, the default name verified in
              the server certificate is obtained from the next-hop domain as
              specified in the smtp_tls_secure_cert_match configuration
              parameter. The default matching rule is that a server
              certificate matches when its name is equal to or is a sub-domain
              of the nexthop domain. This security level is not an appropriate
              default for systems delivering mail to the Internet.

       Examples:

       # No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
       smtp_tls_security_level = none

       # Opportunistic TLS.
       smtp_tls_security_level = may
       # Postfix >= 2.6:
       # Do not tweak opportunistic ciphers or protocol unless it is essential
       # to do so (if a security vulnerability is found in the SSL library that
       # can be mitigated by disabling a particular protocol or raising the
       # cipher grade from "export" to "low" or "medium").
       smtp_tls_ciphers = export
       smtp_tls_protocols = !SSLv2

       # Mandatory (high-grade) TLS encryption.
       smtp_tls_security_level = encrypt
       smtp_tls_mandatory_ciphers = high

       # Mandatory TLS verification of hostname or nexthop domain.
       smtp_tls_security_level = verify
       smtp_tls_mandatory_ciphers = high
       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       # Secure channel TLS with exact nexthop name match.
       smtp_tls_security_level = secure
       smtp_tls_mandatory_protocols = TLSv1
       smtp_tls_mandatory_ciphers = high
       smtp_tls_secure_cert_match = nexthop

       # Certificate fingerprint verification (Postfix >= 2.5).
       # The CA-less "fingerprint" security level only scales to a limited
       # number of destinations. As a global default rather than a per-site
       # setting, this is practical when mail for all recipients is sent
       # to a central mail hub.
       relayhost = [mailhub.example.com]
       smtp_tls_security_level = fingerprint
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       smtp_tls_mandatory_ciphers = high
       smtp_tls_fingerprint_cert_match =
           3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
           EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.3 and later.

smtp_tls_session_cache_database (default: empty)
       Name of the file containing the optional Postfix SMTP client TLS
       session cache. Specify a database type that supports enumeration, such
       as btree or sdbm; there is no need to support concurrent access.  The
       file is created if it does not exist. The smtp(8) daemon does not use
       this parameter directly, rather the cache is implemented indirectly in
       the tlsmgr(8) daemon. This means that per-smtp-instance master.cf
       overrides of this parameter are not effective.  Note, that each of the
       cache databases supported by tlsmgr(8) daemon:
       $smtpd_tls_session_cache_database, $smtp_tls_session_cache_database
       (and with Postfix 2.3 and later $lmtp_tls_session_cache_database),
       needs to be stored separately. It is not at this time possible to store
       multiple caches in a single database.

       Note: dbm databases are not suitable. TLS session objects are too
       large.

       As of version 2.5, Postfix no longer uses root privileges when opening
       this file. The file should now be stored under the Postfix-owned
       data_directory. As a migration aid, an attempt to open the file under a
       non-Postfix directory is redirected to the Postfix-owned
       data_directory, and a warning is logged.

       Example:

       smtp_tls_session_cache_database = btree:/var/db/postfix/smtp_scache

       This feature is available in Postfix 2.2 and later.

smtp_tls_session_cache_timeout (default: 3600s)
       The expiration time of Postfix SMTP client TLS session cache
       information.  A cache cleanup is performed periodically every
       $smtp_tls_session_cache_timeout seconds. As with
       $smtp_tls_session_cache_database, this parameter is implemented in the
       tlsmgr(8) daemon and therefore per-smtp-instance master.cf overrides
       are not possible.

       This feature is available in Postfix 2.2 and later.

smtp_tls_verify_cert_match (default: hostname)
       The server certificate peername verification method for the "verify"
       TLS security level. In a "verify" TLS policy table
       ($smtp_tls_policy_maps) entry the optional "match" attribute overrides
       this main.cf setting.

       This parameter specifies one or more patterns or strategies separated
       by commas, whitespace or colons.  In the policy table the only valid
       separator is the colon character.

       Patterns specify domain names, or domain name suffixes:

       example.com
              Match the example.com domain, i.e. one of the names the server
              certificate must be example.com, upper and lower case
              distinctions are ignored.

       .example.com
              Match subdomains of the example.com domain, i.e. match a name in
              the server certificate that consists of a non-zero number of
              labels followed by a .example.com suffix. Case distinctions are
              ignored.

       Strategies specify a transformation from the next-hop domain to the
       expected name in the server certificate:

       nexthop
              Match against the next-hop domain, which is either the recipient
              domain, or the transport next-hop configured for the domain
              stripped of any optional socket type prefix, enclosing square
              brackets and trailing port. When MX lookups are not suppressed,
              this is the original nexthop domain prior to the MX lookup, not
              the result of the MX lookup. For LMTP delivery via UNIX-domain
              sockets, the verified next-hop name is $myhostname.  This
              strategy is suitable for use with the "secure" policy. Case is
              ignored.

       dot-nexthop
              As above, but match server certificate names that are subdomains
              of the next-hop domain. Case is ignored.

       hostname
              Match against the hostname of the server, often obtained via an
              unauthenticated DNS MX lookup. For LMTP delivery via UNIX-domain
              sockets, the verified name is $myhostname. This matches the
              verification strategy of the "MUST" keyword in the obsolete
              smtp_tls_per_site table, and is suitable for use with the
              "verify" security level. When the next-hop name is enclosed in
              square brackets to suppress MX lookups, the "hostname" strategy
              is the same as the "nexthop" strategy. Case is ignored.

       Sample main.cf setting:

       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       Sample policy table override:

       example.com     verify  match=hostname:nexthop
       .example.com    verify  match=example.com:.example.com:hostname

       This feature is available in Postfix 2.3 and later.

smtp_use_tls (default: no)
       Opportunistic mode: use TLS when a remote SMTP server announces
       STARTTLS support, otherwise send the mail in the clear. Beware: some
       SMTP servers offer STARTTLS even if it is not configured.  With Postfix
       < 2.3, if the TLS handshake fails, and no other server is available,
       delivery is deferred and mail stays in the queue. If this is a concern
       for you, use the smtp_tls_per_site feature instead.

       This feature is available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_security_level instead.

smtp_xforward_timeout (default: 300s)
       The SMTP client time limit for sending the XFORWARD command, and for
       receiving the server response.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_authorized_verp_clients (default: $authorized_verp_clients)
       What SMTP clients are allowed to specify the XVERP command.  This
       command requests that mail be delivered one recipient at a time with a
       per recipient return address.

       By default, no clients are allowed to specify XVERP.

       This parameter was renamed with Postfix version 2.1. The default value
       is backwards compatible with Postfix version 2.0.

       Specify a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the network part
       of a host address. You can also specify hostnames or .domain names (the
       initial dot causes the domain to match any name below it),
       "/file/name" or "type:table" patterns.  A "/file/name" pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table entry matches a lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside [] in
       the smtpd_authorized_verp_clients value, and in files specified with
       "/file/name".  IP version 6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xclient_hosts (default: empty)
       What SMTP clients are allowed to use the XCLIENT feature.  This command
       overrides SMTP client information that is used for access control.
       Typical use is for SMTP-based content filters, fetchmail-like programs,
       or SMTP server access rule testing. See the XCLIENT_README document for
       details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XCLIENT.

       Specify a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the network part
       of a host address. You can also specify hostnames or .domain names (the
       initial dot causes the domain to match any name below it),
       "/file/name" or "type:table" patterns.  A "/file/name" pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table entry matches a lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside [] in
       the smtpd_authorized_xclient_hosts value, and in files specified with
       "/file/name".  IP version 6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xforward_hosts (default: empty)
       What SMTP clients are allowed to use the XFORWARD feature.  This
       command forwards information that is used to improve logging after
       SMTP-based content filters. See the XFORWARD_README document for
       details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XFORWARD.

       Specify a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the network part
       of a host address. You can also specify hostnames or .domain names (the
       initial dot causes the domain to match any name below it),
       "/file/name" or "type:table" patterns.  A "/file/name" pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table entry matches a lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside [] in
       the smtpd_authorized_xforward_hosts value, and in files specified with
       "/file/name".  IP version 6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

smtpd_banner (default: $myhostname ESMTP $mail_name)
       The text that follows the 220 status code in the SMTP greeting banner.
       Some people like to see the mail version advertised. By default,
       Postfix shows no version.

       You MUST specify $myhostname at the start of the text. This is required
       by the SMTP protocol.

       Example:

       smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

smtpd_client_connection_count_limit (default: 50)
       How many simultaneous connections any client is allowed to make to this
       service.  By default, the limit is set to half the default process
       limit value.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

smtpd_client_connection_rate_limit (default: 0)
       The maximal number of connection attempts any client is allowed to make
       to this service per time unit.  The time unit is specified with the
       anvil_rate_time_unit configuration parameter.

       By default, a client can make as many connections per time unit as
       Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_connection_rate_limit = 1000

smtpd_client_event_limit_exceptions (default: $mynetworks)
       Clients that are excluded from smtpd_client_*_count/rate_limit
       restrictions. See the mynetworks parameter description for the
       parameter value syntax.

       By default, clients in trusted networks are excluded. Specify a list of
       network blocks, hostnames or .domain names (the initial dot causes the
       domain to match any name below it).

       Note: IP version 6 address information must be specified inside [] in
       the smtpd_client_event_limit_exceptions value, and in files specified
       with "/file/name".  IP version 6 addresses contain the ":" character,
       and would otherwise be confused with a "type:table" pattern.

       This feature is available in Postfix 2.2 and later.

smtpd_client_message_rate_limit (default: 0)
       The maximal number of message delivery requests that any client is
       allowed to make to this service per time unit, regardless of whether or
       not Postfix actually accepts those messages.  The time unit is
       specified with the anvil_rate_time_unit configuration parameter.

       By default, a client can send as many message delivery requests per
       time unit as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_message_rate_limit = 1000

smtpd_client_new_tls_session_rate_limit (default: 0)
       The maximal number of new (i.e., uncached) TLS sessions that a remote
       SMTP client is allowed to negotiate with this service per time unit.
       The time unit is specified with the anvil_rate_time_unit configuration
       parameter.

       By default, a remote SMTP client can negotiate as many new TLS sessions
       per time unit as Postfix can accept.

       To disable this feature, specify a limit of 0. Otherwise, specify a
       limit that is at least the per-client concurrent session limit, or else
       legitimate client sessions may be rejected.

       WARNING: The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.3 and later.

       Example:

       smtpd_client_new_tls_session_rate_limit = 100

smtpd_client_port_logging (default: no)
       Enable logging of the remote SMTP client port in addition to the
       hostname and IP address. The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

smtpd_client_recipient_rate_limit (default: 0)
       The maximal number of recipient addresses that any client is allowed to
       send to this service per time unit, regardless of whether or not
       Postfix actually accepts those recipients.  The time unit is specified
       with the anvil_rate_time_unit configuration parameter.

       By default, a client can send as many recipient addresses per time unit
       as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_recipient_rate_limit = 1000

smtpd_client_restrictions (default: empty)
       Optional SMTP server access restrictions in the context of a client
       SMTP connection request.  See SMTPD_ACCESS_README, section "Delayed
       evaluation of SMTP access restriction lists" for a discussion of
       evaluation context and time.

       The default is to allow all connection requests.

       Specify a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next line with whitespace.
       Restrictions are applied in the order as specified; the first
       restriction that matches wins.

       The following restrictions are specific to client hostname or client
       network address information.

       check_ccert_access type:table
              Use the client certificate fingerprint as lookup key for the
              specified access(5) database; with Postfix version 2.2, also
              require that the SMTP client certificate is verified
              successfully.  The fingerprint digest algorithm is configurable
              via the smtpd_tls_fingerprint_digest parameter (hard-coded as
              md5 prior to Postfix version 2.5).  This feature is available
              with Postfix version 2.2 and later.

       check_client_access type:table
              Search the specified access database for the client hostname,
              parent domains, client IP address, or networks obtained by
              stripping least significant octets. See the access(5) manual
              page for details.

       check_client_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              client hostname, and execute the corresponding action.  Note: a
              result of "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.  This
              feature is available in Postfix 2.7 and later.

       check_client_ns_access type:table
              Search the specified access(5) database for the DNS servers for
              the client hostname, and execute the corresponding action.
              Note: a result of "OK" is not allowed for safety reasons.
              Instead, use DUNNO in order to exclude specific hosts from
              blacklists.  This feature is available in Postfix 2.7 and later.

       check_reverse_client_hostname_access type:table
              Search the specified access database for the unverified reverse
              client hostname, parent domains, client IP address, or networks
              obtained by stripping least significant octets. See the
              access(5) manual page for details.  Note: a result of "OK" is
              not allowed for safety reasons.  Instead, use DUNNO in order to
              exclude specific hosts from blacklists.  This feature is
              available in Postfix 2.6 and later.

       check_reverse_client_hostname_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              unverified reverse client hostname, and execute the
              corresponding action.  Note: a result of "OK" is not allowed for
              safety reasons.  Instead, use DUNNO in order to exclude specific
              hosts from blacklists.  This feature is available in Postfix 2.7
              and later.

       check_reverse_client_hostname_ns_access type:table
              Search the specified access(5) database for the DNS servers for
              the unverified reverse client hostname, and execute the
              corresponding action.  Note: a result of "OK" is not allowed for
              safety reasons.  Instead, use DUNNO in order to exclude specific
              hosts from blacklists.  This feature is available in Postfix 2.7
              and later.

       permit_inet_interfaces
              Permit the request when the client IP address matches
              $inet_interfaces.

       permit_mynetworks
              Permit the request when the client IP address matches any
              network or network address listed in  $mynetworks.

       permit_sasl_authenticated
              Permit the request when the client is successfully authenticated
              via the RFC 4954 (AUTH) protocol.

       permit_tls_all_clientcerts
              Permit the request when the remote SMTP client certificate is
              verified successfully.  This option must be used only if a
              special CA issues the certificates and only this CA is listed as
              trusted CA. Otherwise, clients with a third-party certificate
              would also be allowed to relay.  Specify "tls_append_default_CA
              = no" when the trusted CA is specified with smtpd_tls_CAfile or
              smtpd_tls_CApath, to prevent Postfix from appending the system-
              supplied default CAs.  This feature is available with Postfix
              version 2.2.

       permit_tls_clientcerts
              Permit the request when the remote SMTP client certificate
              fingerprint is listed in $relay_clientcerts.  The fingerprint
              digest algorithm is configurable via the
              smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior
              to Postfix version 2.5).  This feature is available with Postfix
              version 2.2.

       reject_rbl_client rbl_domain=d.d.d.d
              Reject the request when the reversed client network address is
              listed with the A record "d.d.d.d" under rbl_domain (Postfix
              version 2.1 and later only).  Each "d" is a number, or a pattern
              inside "[]" that contains one or more ";"-separated numbers or
              number..number ranges (Postfix version 2.8 and later).  If no
              "=d.d.d.d" is specified, reject the request when the reversed
              client network address is listed with any A record under
              rbl_domain.
              The maps_rbl_reject_code parameter specifies the response code
              for rejected requests (default:  554), the default_rbl_reply
              parameter specifies the default server reply, and the
              rbl_reply_maps  parameter specifies tables with server replies
              indexed by rbl_domain.  This feature is available in Postfix 2.0
              and later.

       permit_dnswl_client dnswl_domain=d.d.d.d
              Accept the request when the reversed client network address is
              listed with the A record "d.d.d.d" under dnswl_domain.  Each "d"
              is a number, or a pattern inside "[]" that contains one or more
              ";"-separated numbers or number..number ranges.  If no
              "=d.d.d.d" is specified, accept the request when the reversed
              client network address is listed with any A record under
              dnswl_domain.
              For safety, permit_dnswl_client is silently ignored when it
              would override reject_unauth_destination.  The result is
              DEFER_IF_REJECT when whitelist lookup fails.  This feature is
              available in Postfix 2.8 and later.

       reject_rhsbl_client rbl_domain=d.d.d.d
              Reject the request when the client hostname is listed with the A
              record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
              only).  Each "d" is a number, or a pattern inside "[]" that
              contains one or more ";"-separated numbers or number..number
              ranges (Postfix version 2.8 and later).  If no "=d.d.d.d" is
              specified, reject the request when the client hostname is listed
              with any A record under rbl_domain. See the reject_rbl_client
              description above for additional RBL related configuration
              parameters.  This feature is available in Postfix 2.0 and later;
              with Postfix version 2.8 and later, reject_rhsbl_reverse_client
              will usually produce better results.

       permit_rhswl_client rhswl_domain=d.d.d.d
              Accept the request when the client hostname is listed with the A
              record "d.d.d.d" under rhswl_domain.  Each "d" is a number, or a
              pattern inside "[]" that contains one or more ";"-separated
              numbers or number..number ranges. If no "=d.d.d.d" is specified,
              accept the request when the client hostname is listed with any A
              record under rhswl_domain.
              Caution: client name whitelisting is fragile, since the client
              name lookup can fail due to temporary outages.  Client name
              whitelisting should be used only to reduce false positives in
              e.g.  DNS-based blocklists, and not for making access rule
              exceptions.
              For safety, permit_rhswl_client is silently ignored when it
              would override reject_unauth_destination.  The result is
              DEFER_IF_REJECT when whitelist lookup fails.  This feature is
              available in Postfix 2.8 and later.

       reject_rhsbl_reverse_client rbl_domain=d.d.d.d
              Reject the request when the unverified reverse client hostname
              is listed with the A record "d.d.d.d" under rbl_domain.  Each
              "d" is a number, or a pattern inside "[]" that contains one or
              more ";"-separated numbers or number..number ranges.  If no
              "=d.d.d.d" is specified, reject the request when the unverified
              reverse client hostname is listed with any A record under
              rbl_domain. See the reject_rbl_client description above for
              additional RBL related configuration parameters.  This feature
              is available in Postfix 2.8 and later.

       reject_unknown_client_hostname (with Postfix < 2.3:
              reject_unknown_client)
              Reject the request when 1) the client IP address->name mapping
              fails, 2) the name->address mapping fails, or 3) the
              name->address mapping does not match the client IP address.
              This is a stronger restriction than the
              reject_unknown_reverse_client_hostname feature, which triggers
              only under condition 1) above.
              The unknown_client_reject_code parameter specifies the response
              code for rejected requests (default: 450). The reply is always
              450 in case the address->name or name->address lookup failed due
              to a temporary problem.

       reject_unknown_reverse_client_hostname
              Reject the request when the client IP address has no
              address->name mapping.
              This is a weaker restriction than the
              reject_unknown_client_hostname feature, which requires not only
              that the address->name and name->address mappings exist, but
              also that the two mappings reproduce the client IP address.
              The unknown_client_reject_code parameter specifies the response
              code for rejected requests (default: 450).  The reply is always
              450 in case the address->name lookup failed due to a temporary
              problem.
              This feature is available in Postfix 2.3 and later.

       In addition, you can use any of the following generic restrictions.
       These restrictions are applicable in any SMTP command context.

       check_policy_service servername
              Query the specified policy server. See the SMTPD_POLICY_README
              document for details. This feature is available in Postfix 2.1
              and later.

       defer  Defer the request. The client is told to try again later. This
              restriction is useful at the end of a restriction list, to make
              the default policy explicit.
              The defer_code parameter specifies the SMTP server reply code
              (default: 450).

       defer_if_permit
              Defer the request if some later restriction would result in an
              explicit or implicit PERMIT action.  This is useful when a
              blacklisting feature fails due to a temporary problem.  This
              feature is available in Postfix version 2.1 and later.

       defer_if_reject
              Defer the request if some later restriction would result in a
              REJECT action.  This is useful when a whitelisting feature fails
              due to a temporary problem.  This feature is available in
              Postfix version 2.1 and later.

       permit Permit the request. This restriction is useful at the end of a
              restriction list, to make the default policy explicit.

       reject_multi_recipient_bounce
              Reject the request when the envelope sender is the null address,
              and the message has multiple envelope recipients. This usage has
              rare but legitimate applications: under certain conditions,
              multi-recipient mail that was posted with the DSN option
              NOTIFY=NEVER may be forwarded with the null sender address.
              Note: this restriction can only work reliably when used in
              smtpd_data_restrictions or smtpd_end_of_data_restrictions,
              because the total number of recipients is not known at an
              earlier stage of the SMTP conversation.  Use at the RCPT stage
              will only reject the second etc.  recipient.
              The multi_recipient_bounce_reject_code parameter specifies the
              response code for rejected requests (default:  550).  This
              feature is available in Postfix 2.1 and later.

       reject_plaintext_session
              Reject the request when the connection is not encrypted. This
              restriction should not be used before the client has had a
              chance to negotiate encryption with the AUTH or STARTTLS
              commands.
              The plaintext_reject_code parameter specifies the response code
              for rejected requests (default:  450).  This feature is
              available in Postfix 2.3 and later.

       reject_unauth_pipelining
              Reject the request when the client sends SMTP commands ahead of
              time where it is not allowed, or when the client sends SMTP
              commands ahead of time without knowing that Postfix actually
              supports ESMTP command pipelining. This stops mail from bulk
              mail software that improperly uses ESMTP command pipelining in
              order to speed up deliveries.
              With Postfix 2.6 and later, the SMTP server sets a per-session
              flag whenever it detects illegal pipelining, including pipelined
              EHLO or HELO commands. The reject_unauth_pipelining feature
              simply tests whether the flag was set at any point in time
              during the session.
              With older Postfix versions, reject_unauth_pipelining checks the
              current status of the input read queue, and its usage is not
              recommended in contexts other than smtpd_data_restrictions.

       reject Reject the request. This restriction is useful at the end of a
              restriction list, to make the default policy explicit.  The
              reject_code configuration parameter specifies the response code
              for rejected requests (default: 554).

       sleep seconds
              Pause for the specified number of seconds and proceed with the
              next restriction in the list, if any. This may stop zombie mail
              when used as:
              /etc/postfix/main.cf:
                  smtpd_client_restrictions =
                      sleep 1, reject_unauth_pipelining
                  smtpd_delay_reject = no
              This feature is available in Postfix 2.3.

       warn_if_reject
              Change the meaning of the next restriction, so that it logs a
              warning instead of rejecting a request (look for logfile records
              that contain "reject_warning"). This is useful for testing new
              restrictions in a "live" environment without risking unnecessary
              loss of mail.

       Other restrictions that are valid in this context:

       o      SMTP command specific restrictions that are described under the
              smtpd_helo_restrictions, smtpd_sender_restrictions or
              smtpd_recipient_restrictions parameters. When helo, sender or
              recipient restrictions are listed under
              smtpd_client_restrictions, they have effect only with
              "smtpd_delay_reject = yes", so that $smtpd_client_restrictions
              is evaluated at the time of the RCPT TO command.

       Example:

       smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

smtpd_command_filter (default: empty)
       A mechanism to transform commands from remote SMTP clients.  This is a
       last-resort tool to work around client commands that break inter-
       operability with the Postfix SMTP server.  Other uses involve fault
       injection to test Postfix's handling of invalid commands.

       Specify the name of a "type:table" lookup table. The search string is
       the SMTP command as received from the remote SMTP client, except that
       initial whitespace and the trailing <CR><LF> are removed.  The result
       value is executed by the Postfix SMTP server.

       There is no need to use smtpd_command_filter for the following cases:

       o      Use "resolve_numeric_domain = yes" to accept "user@ipaddress".

       o      Postfix already accepts the correct form "user@[ipaddress]". Use
              virtual_alias_maps or canonical_maps to translate these into
              domain names if necessary.

       o      Use "strict_rfc821_envelopes = no" to accept "RCPT TO:<User Name
              &lt;user@example.com&gt;&gt;". Postfix will ignore the "User Name" part
              and deliver to the &lt;user@example.com&gt; address.

       Examples of problems that can be solved with the smtpd_command_filter
       feature:

       /etc/postfix/main.cf:
           smtpd_command_filter = pcre:/etc/postfix/command_filter

       /etc/postfix/command_filter:
           # Work around clients that send malformed HELO commands.
           /^HELO\s*$/ HELO domain.invalid

           # Work around clients that send empty lines.
           /^\s*$/     NOOP

           # Work around clients that send RCPT TO:<'user@domain'>.
           # WARNING: do not lose the parameters that follow the address.
           /^RCPT\s+TO:\s*<'([^[:space:]]+)'>(.*)/     RCPT TO:<$1>$2

           # Bounce-never mail sink. Use notify_classes=bounce,resource,software
           # to send bounced mail to the postmaster (with message body removed).
           /^(RCPT\s+TO:.*?)\bNOTIFY=\S+\b(.*)/ $1 NOTIFY=NEVER $2
           /^(RCPT\s+TO:.*)/                    $1 NOTIFY=NEVER

       This feature is available in Postfix 2.7.

smtpd_data_restrictions (default: empty)
       Optional access restrictions that the Postfix SMTP server applies in
       the context of the SMTP DATA command.  See SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       This feature is available in Postfix 2.0 and later.

       Specify a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next line with whitespace.
       Restrictions are applied in the order as specified; the first
       restriction that matches wins.

       The following restrictions are valid in this context:

       o      Generic restrictions that can be used in any SMTP command
              context, described under smtpd_client_restrictions.

       o      SMTP command specific restrictions described under
              smtpd_client_restrictions, smtpd_helo_restrictions,
              smtpd_sender_restrictions or smtpd_recipient_restrictions.

       o      However, no recipient information is available in the case of
              multi-recipient mail. Acting on only one recipient would be
              misleading, because any decision will affect all recipients
              equally. Acting on all recipients would require a possibly very
              large amount of memory, and would also be misleading for the
              reasons mentioned before.

       Examples:

       smtpd_data_restrictions = reject_unauth_pipelining
       smtpd_data_restrictions = reject_multi_recipient_bounce

smtpd_delay_open_until_valid_rcpt (default: yes)
       Postpone the start of an SMTP mail transaction until a valid RCPT TO
       command is received. Specify "no" to create a mail transaction as soon
       as the SMTP server receives a valid MAIL FROM command.

       With sites that reject lots of mail, the default setting reduces the
       use of disk, CPU and memory resources. The downside is that rejected
       recipients are logged with NOQUEUE instead of a mail transaction ID.
       This complicates the logfile analysis of multi-recipient mail.

       This feature is available in Postfix 2.3 and later.

smtpd_delay_reject (default: yes)
       Wait until the RCPT TO command before evaluating
       $smtpd_client_restrictions, $smtpd_helo_restrictions and
       $smtpd_sender_restrictions, or wait until the ETRN command before
       evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.

       This feature is turned on by default because some clients apparently
       mis-behave when the Postfix SMTP server rejects commands before RCPT
       TO.

       The default setting has one major benefit: it allows Postfix to log
       recipient address information when rejecting a client name/address or
       sender address, so that it is possible to find out whose mail is being
       rejected.

smtpd_discard_ehlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote SMTP client address, with case
       insensitive lists of EHLO keywords (pipelining, starttls, auth, etc.)
       that the SMTP server will not send in the EHLO response to a remote
       SMTP client. See smtpd_discard_ehlo_keywords for details.  The table is
       not searched by hostname for robustness reasons.

       This feature is available in Postfix 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)
       A case insensitive list of EHLO keywords (pipelining, starttls, auth,
       etc.) that the SMTP server will not send in the EHLO response to a
       remote SMTP client.

       This feature is available in Postfix 2.2 and later.

       Notes:

       o      Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

       o      Use the smtpd_discard_ehlo_keyword_address_maps feature to
              discard EHLO keywords selectively.

smtpd_end_of_data_restrictions (default: empty)
       Optional access restrictions that the Postfix SMTP server applies in
       the context of the SMTP END-OF-DATA command.  See SMTPD_ACCESS_README,
       section "Delayed evaluation of SMTP access restriction lists" for a
       discussion of evaluation context and time.

       This feature is available in Postfix 2.2 and later.

       See smtpd_data_restrictions for details and limitations.

smtpd_enforce_tls (default: no)
       Mandatory TLS: announce STARTTLS support to SMTP clients, and require
       that clients use TLS encryption.  According to RFC 2487 this MUST NOT
       be applied in case of a publicly-referenced SMTP server.  This option
       is off by default and should be used only on dedicated servers.

       Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".

       Note 2: when invoked via "sendmail -bs", Postfix will never offer
       STARTTLS due to insufficient privileges to access the server private
       key. This is intended behavior.

       This feature is available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtpd_tls_security_level instead.

smtpd_error_sleep_time (default: 1s)
       With Postfix version 2.1 and later: the SMTP server response delay
       after a client has made more than $smtpd_soft_error_limit errors, and
       fewer than $smtpd_hard_error_limit errors, without delivering mail.

       With Postfix version 2.0 and earlier: the SMTP server delay before
       sending a reject (4xx or 5xx) response, when the client has made fewer
       than $smtpd_soft_error_limit errors without delivering mail.

smtpd_etrn_restrictions (default: empty)
       Optional SMTP server access restrictions in the context of a client
       ETRN request.  See SMTPD_ACCESS_README, section "Delayed evaluation of
       SMTP access restriction lists" for a discussion of evaluation context
       and time.

       The Postfix ETRN implementation accepts only destinations that are
       eligible for the Postfix "fast flush" service. See the ETRN_README file
       for details.

       Specify a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next line with whitespace.
       Restrictions are applied in the order as specified; the first
       restriction that matches wins.

       The following restrictions are specific to the domain name information
       received with the ETRN command.

       check_etrn_access type:table
              Search the specified access database for the ETRN domain name or
              its parent domains. See the access(5) manual page for details.

       Other restrictions that are valid in this context:

       o      Generic restrictions that can be used in any SMTP command
              context, described under smtpd_client_restrictions.

       o      SMTP command specific restrictions described under
              smtpd_client_restrictions and smtpd_helo_restrictions.

       Example:

       smtpd_etrn_restrictions = permit_mynetworks, reject

smtpd_expansion_filter (default: see postconf -d output)
       What characters are allowed in $name expansions of RBL reply templates.
       Characters not in the allowed set are replaced by "_".  Use C like
       escapes to specify special characters such as whitespace.

       This parameter is not subjected to $parameter expansion.

       This feature is available in Postfix 2.0 and later.

smtpd_forbidden_commands (default: CONNECT, GET, POST)
       List of commands that cause the Postfix SMTP server to immediately
       terminate the session with a 221 code. This can be used to disconnect
       clients that obviously attempt to abuse the system. In addition to the
       commands listed in this parameter, commands that follow the "Label:"
       format of message headers will also cause a disconnect.

       This feature is available in Postfix 2.2 and later.

smtpd_hard_error_limit (default: normal: 20, overload: 1)
       The maximal number of errors a remote SMTP client is allowed to make
       without delivering mail. The Postfix SMTP server disconnects when the
       limit is exceeded. Normally the default limit is 20, but it changes
       under overload to just 1. With Postfix 2.5 and earlier, the SMTP server
       always allows up to 20 errors by default.

smtpd_helo_required (default: no)
       Require that a remote SMTP client introduces itself with the HELO or
       EHLO command before sending the MAIL command or other commands that
       require EHLO negotiation.

       Example:

       smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the
       context of the SMTP HELO command.  See SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       The default is to permit everything.

       Note: specify "smtpd_helo_required = yes" to fully enforce this
       restriction (without "smtpd_helo_required = yes", a client can simply
       skip smtpd_helo_restrictions by not sending HELO or EHLO).

       Specify a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next line with whitespace.
       Restrictions are applied in the order as specified; the first
       restriction that matches wins.

       The following restrictions are specific to the hostname information
       received with the HELO or EHLO command.

       check_helo_access type:table
              Search the specified access(5) database for the HELO or EHLO
              hostname or parent domains, and execute the corresponding
              action.  Note: specify "smtpd_helo_required = yes" to fully
              enforce this restriction (without "smtpd_helo_required = yes", a
              client can simply skip check_helo_access by not sending HELO or
              EHLO).

       check_helo_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              HELO or EHLO hostname, and execute the corresponding action.
              Note 1: a result of "OK" is not allowed for safety reasons.
              Instead, use DUNNO in order to exclude specific hosts from
              blacklists.  Note 2: specify "smtpd_helo_required = yes" to
              fully enforce this restriction (without "smtpd_helo_required =
              yes", a client can simply skip check_helo_mx_access by not
              sending HELO or EHLO).  This feature is available in Postfix 2.1
              and later.

       check_helo_ns_access type:table
              Search the specified access(5) database for the DNS servers for
              the HELO or EHLO hostname, and execute the corresponding action.
              Note 1: a result of "OK" is not allowed for safety reasons.
              Instead, use DUNNO in order to exclude specific hosts from
              blacklists.  Note 2: specify "smtpd_helo_required = yes" to
              fully enforce this restriction (without "smtpd_helo_required =
              yes", a client can simply skip check_helo_ns_access by not
              sending HELO or EHLO). This feature is available in Postfix 2.1
              and later.

       reject_invalid_helo_hostname (with Postfix < 2.3:
              reject_invalid_hostname)
              Reject the request when the HELO or EHLO hostname syntax is
              invalid. Note: specify "smtpd_helo_required = yes" to fully
              enforce this restriction (without "smtpd_helo_required = yes", a
              client can simply skip reject_invalid_helo_hostname by not
              sending HELO or EHLO).
              The invalid_hostname_reject_code specifies the response code for
              rejected requests (default: 501).

       reject_non_fqdn_helo_hostname (with Postfix < 2.3:
              reject_non_fqdn_hostname)
              Reject the request when the HELO or EHLO hostname is not in
              fully-qualified domain form, as required by the RFC. Note:
              specify "smtpd_helo_required = yes" to fully enforce this
              restriction (without "smtpd_helo_required = yes", a client can
              simply skip reject_non_fqdn_helo_hostname by not sending HELO or
              EHLO).
              The non_fqdn_reject_code parameter specifies the response code
              for rejected requests (default: 504).

       reject_rhsbl_helo rbl_domain=d.d.d.d
              Reject the request when the HELO or EHLO hostname hostname is
              listed with the A record "d.d.d.d" under rbl_domain (Postfix
              version 2.1 and later only).  Each "d" is a number, or a pattern
              inside "[]" that contains one or more ";"-separated numbers or
              number..number ranges (Postfix version 2.8 and later).  If no
              "=d.d.d.d" is specified, reject the request when the HELO or
              EHLO hostname is listed with any A record under rbl_domain. See
              the reject_rbl_client description for additional RBL related
              configuration parameters.  Note: specify "smtpd_helo_required =
              yes" to fully enforce this restriction (without
              "smtpd_helo_required = yes", a client can simply skip
              reject_rhsbl_helo by not sending HELO or EHLO). This feature is
              available in Postfix 2.0 and later.

       reject_unknown_helo_hostname (with Postfix < 2.3:
              reject_unknown_hostname)
              Reject the request when the HELO or EHLO hostname has no DNS A
              or MX record.
              The unknown_hostname_reject_code parameter specifies the
              numerical response code for rejected requests (default: 450).
              The unknown_helo_hostname_tempfail_action parameter specifies
              the action after a temporary DNS error (default:
              defer_if_permit). Note: specify "smtpd_helo_required = yes" to
              fully enforce this restriction (without "smtpd_helo_required =
              yes", a client can simply skip reject_unknown_helo_hostname by
              not sending HELO or EHLO).

       Other restrictions that are valid in this context:

       o      Generic restrictions that can be used in any SMTP command
              context, described under smtpd_client_restrictions.

       o      Client hostname or network address specific restrictions
              described under smtpd_client_restrictions.

       o      SMTP command specific restrictions described under
              smtpd_sender_restrictions or smtpd_recipient_restrictions.  When
              sender or recipient restrictions are listed under
              smtpd_helo_restrictions, they have effect only with
              "smtpd_delay_reject = yes", so that $smtpd_helo_restrictions is
              evaluated at the time of the RCPT TO command.

       Examples:

       smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
       smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

smtpd_history_flush_threshold (default: 100)
       The maximal number of lines in the Postfix SMTP server command history
       before it is flushed upon receipt of EHLO, RSET, or end of DATA.

smtpd_junk_command_limit (default: normal: 100, overload: 1)
       The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote
       SMTP client can send before the Postfix SMTP server starts to increment
       the error counter with each junk command.  The junk command count is
       reset after mail is delivered.  See also the smtpd_error_sleep_time and
       smtpd_soft_error_limit configuration parameters.  Normally the default
       limit is 100, but it changes under overload to just 1. With Postfix 2.5
       and earlier, the SMTP server always allows up to 100 junk commands by
       default.

smtpd_milters (default: empty)
       A list of Milter (mail filter) applications for new mail that arrives
       via the Postfix smtpd(8) server.  See the MILTER_README document for
       details.

       This feature is available in Postfix 2.3 and later.

smtpd_noop_commands (default: empty)
       List of commands that the Postfix SMTP server replies to with "250 Ok",
       without doing any syntax checks and without changing state.  This list
       overrides any commands built into the Postfix SMTP server.

smtpd_null_access_lookup_key (default: <&lt;>&gt;)
       The lookup key to be used in SMTP access(5) tables instead of the null
       sender address.

smtpd_peername_lookup (default: yes)
       Attempt to look up the remote SMTP client hostname, and verify that the
       name matches the client IP address. A client name is set to "unknown"
       when it cannot be looked up or verified, or when name lookup is
       disabled.  Turning off name lookup reduces delays due to DNS lookup and
       increases the maximal inbound delivery rate.

       This feature is available in Postfix 2.3 and later.

smtpd_policy_service_max_idle (default: 300s)
       The time after which an idle SMTPD policy service connection is closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_max_ttl (default: 1000s)
       The time after which an active SMTPD policy service connection is
       closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_timeout (default: 100s)
       The time limit for connecting to, writing to or receiving from a
       delegated SMTPD policy server.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_ehlo (default: $myhostname)
       How the Postfix SMTP server announces itself to the proxy filter.  By
       default, the Postfix hostname is used.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_filter (default: empty)
       The hostname and TCP port of the mail filtering proxy server.  The
       proxy receives all mail from the Postfix SMTP server, and is supposed
       to give the result to another Postfix SMTP server process.

       Specify "host:port" or "inet:host:port" for a TCP endpoint, or
       "unix:pathname" for a UNIX-domain endpoint. The host can be specified
       as an IP address or as a symbolic name; no MX lookups are done.  When
       no "host" or "host:"  are specified, the local machine is assumed.
       Pathname interpretation is relative to the Postfix queue directory.

       This feature is available in Postfix 2.1 and later.

       The "inet:" and "unix:" prefixes are available in Postfix 2.3 and
       later.

smtpd_proxy_options (default: empty)
       List of options that control how the Postfix SMTP server communicates
       with a before-queue content filter. Specify zero or more of the
       following, separated by comma or whitespace.

       speed_adjust
              Do not connect to a before-queue content filter until an entire
              message has been received. This reduces the number of
              simultaneous before-queue content filter processes.

       NOTE 1: A filter must not selectively reject recipients of a multi-
       recipient message.  Rejecting all recipients is OK, as is accepting all
       recipients.

       NOTE 2: This feature increases the minimum amount of free queue space
       by $message_size_limit. The extra space is needed to save the message
       to a temporary file.

       This feature is available in Postfix 2.7 and later.

smtpd_proxy_timeout (default: 100s)
       The time limit for connecting to a proxy filter and for sending or
       receiving information.  When a connection fails the client gets a
       generic error message while more detailed information is logged to the
       maillog file.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_recipient_limit (default: 1000)
       The maximal number of recipients that the Postfix SMTP server accepts
       per message delivery request.

smtpd_recipient_overshoot_limit (default: 1000)
       The number of recipients that a remote SMTP client can send in excess
       of the limit specified with $smtpd_recipient_limit, before the Postfix
       SMTP server increments the per-session error count for each excess
       recipient.

smtpd_recipient_restrictions (default: permit_mynetworks,
reject_unauth_destination)
       The access restrictions that the Postfix SMTP server applies in the
       context of the RCPT TO command.  See SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       By default, the Postfix SMTP server accepts:

       o      Mail from clients whose IP address matches $mynetworks, or:

       o      Mail to remote destinations that match $relay_domains, except
              for addresses that contain sender-specified routing
              (user@elsewhere@domain), or:

       o      Mail to local destinations that match $inet_interfaces or
              $proxy_interfaces, $mydestination, $virtual_alias_domains, or
              $virtual_mailbox_domains.

       IMPORTANT: If you change this parameter setting, you must specify at
       least one of the following restrictions. Otherwise Postfix will refuse
       to receive mail:

           reject, defer, defer_if_permit, reject_unauth_destination

       Specify a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next line with whitespace.
       Restrictions are applied in the order as specified; the first
       restriction that matches wins.

       The following restrictions are specific to the recipient address that
       is received with the RCPT TO command.

       check_recipient_access type:table
              Search the specified access(5) database for the resolved RCPT TO
              address, domain, parent domains, or localpart@, and execute the
              corresponding action.

       check_recipient_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              RCPT TO domain, and execute the corresponding action.  Note: a
              result of "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.  This
              feature is available in Postfix 2.1 and later.

       check_recipient_ns_access type:table
              Search the specified access(5) database for the DNS servers for
              the RCPT TO domain, and execute the corresponding action.  Note:
              a result of "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.  This
              feature is available in Postfix 2.1 and later.

       permit_auth_destination
              Permit the request when one of the following is true:

       o      Postfix is mail forwarder: the resolved RCPT TO domain matches
              $relay_domains or a subdomain thereof, and the address contains
              no sender-specified routing (user@elsewhere@domain),

       o      Postfix is the final destination: the resolved RCPT TO domain
              matches $mydestination, $inet_interfaces, $proxy_interfaces,
              $virtual_alias_domains, or $virtual_mailbox_domains, and the
              address contains no sender-specified routing
              (user@elsewhere@domain).

       permit_mx_backup
              Permit the request when the local mail system is backup MX for
              the RCPT TO domain, or when the domain is an authorized
              destination (see permit_auth_destination for definition).

       o      Safety: permit_mx_backup does not accept addresses that have
              sender-specified routing information (example:
              user@elsewhere@domain).

       o      Safety: permit_mx_backup can be vulnerable to mis-use when
              access is not restricted with permit_mx_backup_networks.

       o      Safety: as of Postfix version 2.3, permit_mx_backup no longer
              accepts the address when the local mail system is primary MX for
              the recipient domain.  Exception: permit_mx_backup accepts the
              address when it specifies an authorized destination (see
              permit_auth_destination for definition).

       o      Limitation: mail may be rejected in case of a temporary DNS
              lookup problem with Postfix prior to version 2.0.

       reject_non_fqdn_recipient
              Reject the request when the RCPT TO address is not in fully-
              qualified domain form, as required by the RFC.
              The non_fqdn_reject_code parameter specifies the response code
              for rejected requests (default: 504).

       reject_rhsbl_recipient rbl_domain=d.d.d.d
              Reject the request when the RCPT TO domain is listed with the A
              record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
              only).  Each "d" is a number, or a pattern inside "[]" that
              contains one or more ";"-separated numbers or number..number
              ranges (Postfix version 2.8 and later). If no "=d.d.d.d" is
              specified, reject the request when the RCPT TO domain is listed
              with any A record under rbl_domain.
              The maps_rbl_reject_code parameter specifies the response code
              for rejected requests (default: 554); the default_rbl_reply
              parameter specifies the default server reply; and the
              rbl_reply_maps parameter specifies tables with server replies
              indexed by rbl_domain.  This feature is available in Postfix
              version 2.0 and later.

       reject_unauth_destination
              Reject the request unless one of the following is true:

       o      Postfix is mail forwarder: the resolved RCPT TO domain matches
              $relay_domains or a subdomain thereof, and contains no sender-
              specified routing (user@elsewhere@domain),

       o      Postfix is the final destination: the resolved RCPT TO domain
              matches $mydestination, $inet_interfaces, $proxy_interfaces,
              $virtual_alias_domains, or $virtual_mailbox_domains, and
              contains no sender-specified routing (user@elsewhere@domain).
               The relay_domains_reject_code parameter specifies the
              response code for rejected requests (default: 554).

       reject_unknown_recipient_domain
              Reject the request when Postfix is not final destination for the
              recipient domain, and the RCPT TO domain has no DNS A or MX
              record, or when it has a malformed MX record such as a record
              with a zero-length MX hostname (Postfix version 2.3 and later).
              The unknown_address_reject_code parameter specifies the
              numerical response code for rejected requests (default: 450).
              The response is always 450 in case of a temporary DNS error.
              The unknown_address_tempfail_action parameter specifies the
              action after a temporary DNS error (default: defer_if_permit).

       reject_unlisted_recipient (with Postfix version 2.0:
              check_recipient_maps)
              Reject the request when the RCPT TO address is not listed in the
              list of valid recipients for its domain class. See the
              smtpd_reject_unlisted_recipient parameter description for
              details.  This feature is available in Postfix 2.1 and later.

       reject_unverified_recipient
              Reject the request when mail to the RCPT TO address is known to
              bounce, or when the recipient address destination is not
              reachable.  Address verification information is managed by the
              verify(8) server; see the ADDRESS_VERIFICATION_README file for
              details.
              The unverified_recipient_reject_code parameter specifies the
              numerical response code when an address is known to bounce
              (default: 450, change into 550 when you are confident that it is
              safe to do so).
              The unverified_recipient_defer_code parameter specifies the
              numerical response code when an address probe failed due to a
              temporary problem (default: 450).
              The unverified_recipient_tempfail_action parameter specifies the
              action after addres probe failure due to a temporary problem
              (default: defer_if_permit).
              This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       o      Generic restrictions that can be used in any SMTP command
              context, described under smtpd_client_restrictions.

       o      SMTP command specific restrictions described under
              smtpd_client_restrictions, smtpd_helo_restrictions and
              smtpd_sender_restrictions.

       Example:

       smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_footer (default: empty)
       Optional information that is appended after each SMTP server 4XX or 5XX
       response.

       Example:

       /etc/postfix/main.cf:
           smtpd_reject_footer = For assistance, call 800-555-0101.
            Please provide the following information in your problem report:
            time ($localtime), client ($client_address) and server
            ($server_name).

       Server response:

           550-5.5.1 <user@example> Recipient address rejected: User unknown
           550 5.5.1 For assistance, call 800-555-0101. Please provide the
           following information in your problem report: time (Jan 4 15:42:00),
           client (192.168.1.248) and server (mail1.example.com).

       Note: the above text is meant to make it easier to find the Postfix
       logfile records for a failed SMTP session. The text itself is not
       logged to the Postfix SMTP server's maillog file.

       Be sure to keep the text as short as possible. Long text may be
       truncated before it is logged to the remote SMTP client's maillog file,
       or before it is returned to the sender in a delivery status
       notification.

       This feature supports a limited number of $name attributes in the
       footer text. These are replaced by their current value for the SMTP
       session:

       client_address
              The Client IP address that is logged in the maillog file.

       client_port
              The client TCP port that is logged in the maillog file.

       localtime
              The server local time (Mmm dd hh:mm:ss) that is logged in the
              maillog file.

       server_name
              The server's myhostname value.  This attribute is made available
              for sites with multiple MTAs (perhaps behind a load-balancer),
              where the server name can help the server support team to
              quickly find the right log files.

       Notes:

       o      NOT SUPPORTED are other attributes such as sender, recipient, or
              main.cf parameters.

       o      For safety reasons, text that does not match
              $smtpd_expansion_filter is censored.

       This feature supports the two-character sequence \n as a request for a
       line break in the footer text. Postfix automatically inserts after each
       line break the three-digit SMTP reply code (and optional enhanced
       status code) from the original Postfix reject message.

       This feature is available in Postfix 2.8 and later.

smtpd_reject_unlisted_recipient (default: yes)
       Request that the Postfix SMTP server rejects mail for unknown recipient
       addresses, even when no explicit reject_unlisted_recipient access
       restriction is specified. This prevents the Postfix queue from filling
       up with undeliverable MAILER-DAEMON messages.

       An address is always considered "known" when it matches a virtual(5)
       alias or a canonical(5) mapping.

       o      The recipient domain matches $mydestination, $inet_interfaces or
              $proxy_interfaces, but the recipient is not listed in
              $local_recipient_maps, and $local_recipient_maps is not null.

       o      The recipient domain matches $virtual_alias_domains but the
              recipient is not listed in $virtual_alias_maps.

       o      The recipient domain matches $virtual_mailbox_domains but the
              recipient is not listed in $virtual_mailbox_maps, and
              $virtual_mailbox_maps is not null.

       o      The recipient domain matches $relay_domains but the recipient is
              not listed in $relay_recipient_maps, and $relay_recipient_maps
              is not null.

       This feature is available in Postfix 2.1 and later.

smtpd_reject_unlisted_sender (default: no)
       Request that the Postfix SMTP server rejects mail from unknown sender
       addresses, even when no explicit reject_unlisted_sender access
       restriction is specified. This can slow down an explosion of forged
       mail from worms or viruses.

       An address is always considered "known" when it matches a virtual(5)
       alias or a canonical(5) mapping.

       o      The sender domain matches $mydestination, $inet_interfaces or
              $proxy_interfaces, but the sender is not listed in
              $local_recipient_maps, and $local_recipient_maps is not null.

       o      The sender domain matches $virtual_alias_domains but the sender
              is not listed in $virtual_alias_maps.

       o      The sender domain matches $virtual_mailbox_domains but the
              sender is not listed in $virtual_mailbox_maps, and
              $virtual_mailbox_maps is not null.

       o      The sender domain matches $relay_domains but the sender is not
              listed in $relay_recipient_maps, and $relay_recipient_maps is
              not null.

       This feature is available in Postfix 2.1 and later.

smtpd_restriction_classes (default: empty)
       User-defined aliases for groups of access restrictions. The aliases can
       be specified in smtpd_recipient_restrictions etc., and on the right-
       hand side of a Postfix access(5) table.

       One major application is for implementing per-recipient UCE control.
       See the RESTRICTION_CLASS_README document for other examples.

smtpd_sasl_application_name (default: smtpd)
       The application name that the Postfix SMTP server uses for SASL server
       initialization. This controls the name of the SASL configuration file.
       The default value is smtpd, corresponding to a SASL configuration file
       named smtpd.conf.

       This feature is available in Postfix 2.1 and 2.2. With Postfix 2.3 it
       was renamed to smtpd_sasl_path.

smtpd_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix SMTP server. By default, the
       Postfix SMTP server does not use authentication.

       If a remote SMTP client is authenticated, the permit_sasl_authenticated
       access restriction can be used to permit relay access, like this:

           smtpd_recipient_restrictions =
               permit_mynetworks, permit_sasl_authenticated, ...

       To reject all SMTP connections from unauthenticated clients, specify
       "smtpd_delay_reject = yes" (which is the default) and use:

           smtpd_client_restrictions = permit_sasl_authenticated, reject

       See the SASL_README file for SASL configuration and operation details.

smtpd_sasl_authenticated_header (default: no)
       Report the SASL authenticated user name in the smtpd(8) Received
       message header.

       This feature is available in Postfix 2.3 and later.

smtpd_sasl_exceptions_networks (default: empty)
       What remote SMTP clients the Postfix SMTP server will not offer AUTH
       support to.

       Some clients (Netscape 4 at least) have a bug that causes them to
       require a login and password whenever AUTH is offered, whether it's
       necessary or not. To work around this, specify, for example,
       $mynetworks to prevent Postfix from offering AUTH to local clients.

       Specify a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the network part
       of a host address. You can also "/file/name" or "type:table" patterns.
       A "/file/name" pattern is replaced by its contents; a "type:table"
       lookup table is matched when a table entry matches a lookup string (the
       lookup result is ignored).  Continue long lines by starting the next
       line with whitespace. Specify "!pattern" to exclude an address or
       network block from the list.  The form "!/file/name" is supported only
       in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside [] in
       the smtpd_sasl_exceptions_networks value, and in files specified with
       "/file/name".  IP version 6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

       Example:

       smtpd_sasl_exceptions_networks = $mynetworks

       This feature is available in Postfix 2.1 and later.

smtpd_sasl_local_domain (default: empty)
       The name of the Postfix SMTP server's local SASL authentication realm.

       By default, the local authentication realm name is the null string.

       Examples:

       smtpd_sasl_local_domain = $mydomain
       smtpd_sasl_local_domain = $myhostname

smtpd_sasl_path (default: smtpd)
       Implementation-specific information that the Postfix SMTP server passes
       through to the SASL plug-in implementation that is selected with
       smtpd_sasl_type.  Typically this specifies the name of a configuration
       file or rendezvous point.

       This feature is available in Postfix 2.3 and later. In earlier releases
       it was called smtpd_sasl_application_name.

smtpd_sasl_security_options (default: noanonymous)
       Postfix SMTP server SASL security options; as of Postfix 2.3 the list
       of available features depends on the SASL server implementation that is
       selected with smtpd_sasl_type.

       The following security features are defined for the cyrus server SASL
       implementation:

       Restrict what authentication mechanisms the Postfix SMTP server will
       offer to the client.  The list of available authentication mechanisms
       is system dependent.

       Specify zero or more of the following:

       noplaintext
              Disallow methods that use plaintext passwords.

       noactive
              Disallow methods subject to active (non-dictionary) attack.

       nodictionary
              Disallow methods subject to passive (dictionary) attack.

       noanonymous
              Disallow methods that allow anonymous authentication.

       forward_secrecy
              Only allow methods that support forward secrecy (Dovecot only).

       mutual_auth
              Only allow methods that provide mutual authentication (not
              available with Cyrus SASL version 1).

       By default, the Postfix SMTP server accepts plaintext passwords but not
       anonymous logins.

       Warning: it appears that clients try authentication methods in the
       order as advertised by the server (e.g., PLAIN ANONYMOUS CRAM-MD5)
       which means that if you disable plaintext passwords, clients will log
       in anonymously, even when they should be able to use CRAM-MD5.  So, if
       you disable plaintext logins, disable anonymous logins too.  Postfix
       treats anonymous login as no authentication.

       Example:

       smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)
       The SASL authentication security options that the Postfix SMTP server
       uses for TLS encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtpd_sasl_type (default: cyrus)
       The SASL plug-in type that the Postfix SMTP server should use for
       authentication. The available types are listed with the "postconf -a"
       command.

       This feature is available in Postfix 2.3 and later.

smtpd_sender_login_maps (default: empty)
       Optional lookup table with the SASL login names that own sender (MAIL
       FROM) addresses.

       Specify zero or more "type:table" lookup tables. With lookups from
       indexed files such as DB or DBM, or from networked tables such as NIS,
       LDAP or SQL, the following search operations are done with a sender
       address of user@domain:

       1) user@domain
              This table lookup is always done and has the highest precedence.

       2) user
              This table lookup is done only when the domain part of the
              sender address matches $myorigin, $mydestination,
              $inet_interfaces or $proxy_interfaces.

       3) @domain
              This table lookup is done last and has the lowest precedence.

       In all cases the result of table lookup must be either "not found" or a
       list of SASL login names separated by comma and/or whitespace.

smtpd_sender_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the
       context of the MAIL FROM command.  See SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       The default is to permit everything.

       Specify a list of restrictions, separated by commas and/or whitespace.
       Continue long lines by starting the next line with whitespace.
       Restrictions are applied in the order as specified; the first
       restriction that matches wins.

       The following restrictions are specific to the sender address received
       with the MAIL FROM command.

       check_sender_access type:table
              Search the specified access(5) database for the MAIL FROM
              address, domain, parent domains, or localpart@, and execute the
              corresponding action.

       check_sender_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              MAIL FROM address, and execute the corresponding action.  Note:
              a result of "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.  This
              feature is available in Postfix 2.1 and later.

       check_sender_ns_access type:table
              Search the specified access(5) database for the DNS servers for
              the MAIL FROM address, and execute the corresponding action.
              Note: a result of "OK" is not allowed for safety reasons.
              Instead, use DUNNO in order to exclude specific hosts from
              blacklists.  This feature is available in Postfix 2.1 and later.

       reject_authenticated_sender_login_mismatch
              Enforces the reject_sender_login_mismatch restriction for
              authenticated clients only. This feature is available in Postfix
              version 2.1 and later.

       reject_non_fqdn_sender
              Reject the request when the MAIL FROM address is not in fully-
              qualified domain form, as required by the RFC.
              The non_fqdn_reject_code parameter specifies the response code
              for rejected requests (default: 504).

       reject_rhsbl_sender rbl_domain=d.d.d.d
              Reject the request when the MAIL FROM domain is listed with the
              A record "d.d.d.d" under rbl_domain (Postfix version 2.1 and
              later only).  Each "d" is a number, or a pattern inside "[]"
              that contains one or more ";"-separated numbers or
              number..number ranges (Postfix version 2.8 and later). If no
              "=d.d.d.d" is specified, reject the request when the MAIL FROM
              domain is listed with any A record under rbl_domain.
              The maps_rbl_reject_code parameter specifies the response code
              for rejected requests (default:  554); the default_rbl_reply
              parameter specifies the default server reply; and the
              rbl_reply_maps parameter specifies tables with server replies
              indexed by rbl_domain.  This feature is available in Postfix 2.0
              and later.

       reject_sender_login_mismatch
              Reject the request when $smtpd_sender_login_maps specifies an
              owner for the MAIL FROM address, but the client is not (SASL)
              logged in as that MAIL FROM address owner; or when the client is
              (SASL) logged in, but the client login name doesn't own the MAIL
              FROM address according to $smtpd_sender_login_maps.

       reject_unauthenticated_sender_login_mismatch
              Enforces the reject_sender_login_mismatch restriction for
              unauthenticated clients only. This feature is available in
              Postfix version 2.1 and later.

       reject_unknown_sender_domain
              Reject the request when Postfix is not final destination for the
              sender address, and the MAIL FROM address has no DNS A or MX
              record, or when it has a malformed MX record such as a record
              with a zero-length MX hostname (Postfix version 2.3 and later).
              The unknown_address_reject_code parameter specifies the
              numerical response code for rejected requests (default: 450).
              The response is always 450 in case of a temporary DNS error.
              The unknown_address_tempfail_action parameter specifies the
              action after a temporary DNS error (default: defer_if_permit).

       reject_unlisted_sender
              Reject the request when the MAIL FROM address is not listed in
              the list of valid recipients for its domain class. See the
              smtpd_reject_unlisted_sender parameter description for details.
              This feature is available in Postfix 2.1 and later.

       reject_unverified_sender
              Reject the request when mail to the MAIL FROM address is known
              to bounce, or when the sender address destination is not
              reachable.  Address verification information is managed by the
              verify(8) server; see the ADDRESS_VERIFICATION_README file for
              details.
              The unverified_sender_reject_code parameter specifies the
              numerical response code when an address is known to bounce
              (default: 450, change into 550 when you are confident that it is
              safe to do so).
              The unverified_sender_defer_code specifies the numerical
              response code when an address address probe failed due to a
              temporary problem (default: 450).
              The unverified_sender_tempfail_action parameter specifies the
              action after address probe failure due to a temporary problem
              (default: defer_if_permit).
              This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

       o      Generic restrictions that can be used in any SMTP command
              context, described under smtpd_client_restrictions.

       o      SMTP command specific restrictions described under
              smtpd_client_restrictions and smtpd_helo_restrictions.

       o      SMTP command specific restrictions described under
              smtpd_recipient_restrictions. When recipient restrictions are
              listed under smtpd_sender_restrictions, they have effect only
              with "smtpd_delay_reject = yes", so that
              $smtpd_sender_restrictions is evaluated at the time of the RCPT
              TO command.

       Examples:

       smtpd_sender_restrictions = reject_unknown_sender_domain
       smtpd_sender_restrictions = reject_unknown_sender_domain,
           check_sender_access hash:/etc/postfix/access

smtpd_service_name (default: smtpd)
       The internal service that postscreen(8) forwards allowed connections
       to. In a future version there may be different classes of SMTP service.

       This feature is available in Postfix 2.8.

smtpd_soft_error_limit (default: 10)
       The number of errors a remote SMTP client is allowed to make without
       delivering mail before the Postfix SMTP server slows down all its
       responses.

       o      With Postfix version 2.1 and later, the Postfix SMTP server
              delays all responses by $smtpd_error_sleep_time seconds.

       o      With Postfix versions 2.0 and earlier, the Postfix SMTP server
              delays all responses by (number of errors) seconds.

smtpd_starttls_timeout (default: see postconf -d output)
       The time limit for Postfix SMTP server write and read operations during
       TLS startup and shutdown handshake procedures. The current default
       value is stress-dependent. Before Postfix version 2.8, it was fixed at
       300s.

       This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: normal: 300s, overload: 10s)
       The time limit for sending a Postfix SMTP server response and for
       receiving a remote SMTP client request. Normally the default limit is
       300s, but it changes under overload to just 10s. With Postfix 2.5 and
       earlier, the SMTP server always uses a time limit of 300s by default.

       Note: if you set SMTP time limits to very large values you may have to
       update the global ipc_timeout parameter.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtpd_tls_CAfile (default: empty)
       A file containing (PEM format) CA certificates of root CAs trusted to
       sign either remote SMTP client certificates or intermediate CA
       certificates.  These are loaded into memory before the smtpd(8) server
       enters the chroot jail. If the number of trusted roots is large,
       consider using smtpd_tls_CApath instead, but note that the latter
       directory must be present in the chroot jail if the smtpd(8) server is
       chrooted. This file may also be used to augment the server certificate
       trust chain, but it is best to include all the required certificates
       directly in the server certificate file.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party certificates.

       By default (see smtpd_tls_ask_ccert), client certificates are not
       requested, and smtpd_tls_CAfile should remain empty. If you do make use
       of client certificates, the distinguished names (DNs) of the
       certificate authorities listed in smtpd_tls_CAfile are sent to the
       remote SMTP client in the client certificate request message. MUAs with
       multiple client certificates may use the list of preferred certificate
       authorities to select the correct client certificate.  You may want to
       put your "preferred" CA or CAs in this file, and install other trusted
       CAs in $smtpd_tls_CApath.

       Example:

       smtpd_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)
       A directory containing (PEM format) CA certificates of root CAs trusted
       to sign either remote SMTP client certificates or intermediate CA
       certificates. Do not forget to create the necessary "hash" links with,
       for example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs". To use
       smtpd_tls_CApath in chroot mode, this directory (or a copy) must be
       inside the chroot jail.

       Specify "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party certificates.

       By default (see smtpd_tls_ask_ccert), client certificates are not
       requested, and smtpd_tls_CApath should remain empty. In contrast to
       smtpd_tls_CAfile, DNs of certificate authorities installed in
       $smtpd_tls_CApath are not included in the client certificate request
       message. MUAs with multiple client certificates may use the list of
       preferred certificate authorities to select the correct client
       certificate.  You may want to put your "preferred" CA or CAs in
       $smtpd_tls_CAfile, and install the remaining trusted CAs in
       $smtpd_tls_CApath.

       Example:

       smtpd_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtpd_tls_always_issue_session_ids (default: yes)
       Force the Postfix SMTP server to issue a TLS session id, even when TLS
       session caching is turned off (smtpd_tls_session_cache_database is
       empty). This behavior is compatible with Postfix < 2.3.

       With Postfix 2.3 and later the Postfix SMTP server can disable session
       id generation when TLS session caching is turned off. This keeps
       clients from caching sessions that almost certainly cannot be re-used.

       By default, the Postfix SMTP server always generates TLS session ids.
       This works around a known defect in mail client applications such as MS
       Outlook, and may also prevent interoperability issues with other MTAs.

       Example:

       smtpd_tls_always_issue_session_ids = no

       This feature is available in Postfix 2.3 and later.

smtpd_tls_ask_ccert (default: no)
       Ask a remote SMTP client for a client certificate. This information is
       needed for certificate based mail relaying with, for example, the
       permit_tls_clientcerts feature.

       Some clients such as Netscape will either complain if no certificate is
       available (for the list of CAs in $smtpd_tls_CAfile) or will offer
       multiple client certificates to choose from. This may be annoying, so
       this option is "off" by default.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_auth_only (default: no)
       When TLS encryption is optional in the Postfix SMTP server, do not
       announce or accept SASL authentication over unencrypted connections.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_ccert_verifydepth (default: 9)
       The verification depth for remote SMTP client certificates. A depth of
       1 is sufficient if the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for
       compatibility with earlier Postfix behavior. Prior to Postfix 2.5, the
       default value was 5, but the limit was not actually enforced. If you
       have set this to a lower non-default value, certificates with longer
       trust chains may now fail to verify. Certificate chains with 1 or 2 CAs
       are common, deeper chains are more rare and any number between 5 and 9
       should suffice in practice. You can choose a lower number if, for
       example, you trust certificates directly signed by an issuing CA but
       not any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cert_file (default: empty)
       File with the Postfix SMTP server RSA certificate in PEM format.  This
       file may also contain the Postfix SMTP server private RSA key.

       Public Internet MX hosts without certificates signed by a "reputable"
       CA must generate, and be prepared to present to most clients, a self-
       signed or private-CA signed certificate. The client will not be able to
       authenticate the server, but unless it is running Postfix 2.3 or
       similar software, it will still insist on a server certificate.

       For servers that are not public Internet MX hosts, Postfix 2.3 supports
       configurations with no certificates. This entails the use of just the
       anonymous TLS ciphers, which are not supported by typical SMTP clients.
       Since such clients will not, as a rule, fall back to plain text after a
       TLS handshake failure, the server will be unable to receive email from
       TLS enabled clients. To avoid accidental configurations with no
       certificates, Postfix 2.3 enables certificate-less operation only when
       the administrator explicitly sets "smtpd_tls_cert_file = none". This
       ensures that new Postfix configurations will not accidentally run with
       no certificates.

       Both RSA and DSA certificates are supported.  When both types are
       present, the cipher used determines which certificate will be presented
       to the client.  For Netscape and OpenSSL clients without special cipher
       choices the RSA certificate is preferred.

       To enable a remote SMTP client to verify the Postfix SMTP server
       certificate, the issuing CA certificates must be made available to the
       client. You should include the required certificates in the server
       certificate file, the server certificate first, then the issuing CA(s)
       (bottom-up order).

       Example: the certificate for "server.example.com" was issued by
       "intermediate CA" which itself has a certificate of "root CA".  Create
       the server.pem file with "cat server_cert.pem intermediate_CA.pem
       root_CA.pem > server.pem".

       If you also want to verify client certificates issued by these CAs, you
       can add the CA certificates to the smtpd_tls_CAfile, in which case it
       is not necessary to have them in the smtpd_tls_cert_file or
       smtpd_tls_dcert_file.

       A certificate supplied here must be usable as an SSL server certificate
       and hence pass the "openssl verify -purpose sslserver ..." test.

       Example:

       smtpd_tls_cert_file = /etc/postfix/server.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cipherlist (default: empty)
       Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher
       list. It is easy to create inter-operability problems by choosing a
       non-default cipher list. Do not use a non-default TLS cipherlist for MX
       hosts on the public Internet. Clients that begin the TLS handshake, but
       are unable to agree on a common cipher, may not be able to send any
       email to the SMTP server. Using a restricted cipher list may be more
       appropriate for a dedicated MSA or an internal mailhub, where one can
       exert some control over the TLS software and settings of the connecting
       clients.

       Note: do not use "" quotes around the parameter value.

       This feature is available with Postfix version 2.2. It is not used with
       Postfix 2.3 and later; use smtpd_tls_mandatory_ciphers instead.

smtpd_tls_ciphers (default: export)
       The minimum TLS cipher grade that the Postfix SMTP server will use with
       opportunistic TLS encryption. Cipher types listed in
       smtpd_tls_exclude_ciphers are excluded from the base definition of the
       selected cipher grade. The default value "export" ensures maximum
       inter-operability. Because encryption is optional, stronger controls
       are not appropriate, and this setting SHOULD NOT be changed unless the
       change is essential.

       When TLS is mandatory the cipher grade is chosen via the
       smtpd_tls_mandatory_ciphers configuration parameter, see there for
       syntax details.

       Example:
       smtpd_tls_ciphers = export

       This feature is available in Postfix 2.6 and later. With earlier
       Postfix releases only the smtpd_tls_mandatory_ciphers parameter is
       implemented, and opportunistic TLS always uses "export" or better (i.e.
       all) ciphers.

smtpd_tls_dcert_file (default: empty)
       File with the Postfix SMTP server DSA certificate in PEM format.  This
       file may also contain the Postfix SMTP server private DSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_dh1024_param_file (default: empty)
       File with DH parameters that the Postfix SMTP server should use with
       EDH ciphers.

       Instead of using the exact same parameter sets as distributed with
       other TLS packages, it is more secure to generate your own set of
       parameters with something like the following command:

           openssl gendh -out /etc/postfix/dh_1024.pem -2 1024

       Your actual source for entropy may differ. Some systems have
       /dev/random; on other system you may consider using the "Entropy
       Gathering Daemon EGD", available at http://egd.sourceforge.net/

       Example:

       smtpd_tls_dh1024_param_file = /etc/postfix/dh_1024.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dh512_param_file (default: empty)
       File with DH parameters that the Postfix SMTP server should use with
       EDH ciphers.

       See also the discussion under the smtpd_tls_dh1024_param_file
       configuration parameter.

       Example:

       smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)
       File with the Postfix SMTP server DSA private key in PEM format.  This
       file may be combined with the Postfix SMTP server DSA certificate file
       specified with $smtpd_tls_dcert_file.

       The private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_eccert_file (default: empty)
       File with the Postfix SMTP server ECDSA certificate in PEM format.
       This file may also contain the Postfix SMTP server private ECDSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_eccert_file = /etc/postfix/ecdsa-scert.pem

       This feature is available in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file)
       File with the Postfix SMTP server ECDSA private key in PEM format.
       This file may be combined with the Postfix SMTP server ECDSA
       certificate file specified with $smtpd_tls_eccert_file.

       The private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eecdh_grade (default: see postconf -d output)
       The Postfix SMTP server security grade for ephemeral elliptic-curve
       Diffie-Hellman (EECDH) key exchange.

       The available choices are:

       none   Don't use EECDH. Ciphers based on EECDH key exchange will be
              disabled. This is the default in Postfix versions 2.6 and 2.7.

       strong Use EECDH with approximately 128 bits of security at a
              reasonable computational cost. This is the current best-practice
              trade-off between security and computational efficiency. This is
              the default in Postfix version 2.8 and later.

       ultra  Use EECDH with approximately 192 bits of security at
              computational cost that is approximately twice as high as 128
              bit strength ECC. Barring significant progress in attacks on
              elliptic curve crypto-systems, the "strong" curve is sufficient
              for most users.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later.

smtpd_tls_exclude_ciphers (default: empty)
       List of ciphers or cipher types to exclude from the SMTP server cipher
       list at all TLS security levels. Excluding valid ciphers can create
       interoperability problems. DO NOT exclude ciphers unless it is
       essential to do so. This is not an OpenSSL cipherlist; it is a simple
       list separated by whitespace and/or commas. The elements are a single
       cipher, or one or more "+" separated cipher properties, in which case
       only ciphers matching all the properties are excluded.

       Examples (some of these will cause problems):

           smtpd_tls_exclude_ciphers = aNULL
           smtpd_tls_exclude_ciphers = MD5, DES
           smtpd_tls_exclude_ciphers = DES+MD5
           smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
           smtpd_tls_exclude_ciphers = kEDH+aRSA

       The first setting disables anonymous ciphers. The next setting disables
       ciphers that use the MD5 digest algorithm or the (single) DES
       encryption algorithm. The next setting disables ciphers that use MD5
       and DES together.  The next setting disables the two ciphers
       "AES256-SHA" and "DES-CBC3-MD5". The last setting disables ciphers that
       use "EDH" key exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_fingerprint_digest (default: md5)
       The message digest algorithm used to construct client-certificate
       fingerprints for check_ccert_access and permit_tls_clientcerts. The
       default algorithm is md5, for backwards compatibility with Postfix
       releases prior to 2.5.

       The best practice algorithm is now sha1. Recent advances in hash
       function cryptanalysis have led to md5 being deprecated in favor of
       sha1.  However, as long as there are no known "second pre-image"
       attacks against md5, its use in this context can still be considered
       safe.

       While additional digest algorithms are often available with OpenSSL's
       libcrypto, only those used by libssl in SSL cipher suites are available
       to Postfix. For now this means just md5 or sha1.

       To find the fingerprint of a specific certificate file, with a specific
       digest algorithm, run:

           $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The text to the right of "=" sign is the desired fingerprint.  For
       example:

           $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
           SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       Example: client-certificate access table, with sha1 fingerprints:

           /etc/postfix/main.cf:
               smtpd_tls_fingerprint_digest = sha1
               smtpd_client_restrictions =
                   check_ccert_access hash:/etc/postfix/access,
                   reject
           /etc/postfix/access:
               # Action folded to next line...
               AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
                   OK
               85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
                   permit_auth_destination

       This feature is available in Postfix 2.5 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)
       File with the Postfix SMTP server RSA private key in PEM format.  This
       file may be combined with the Postfix SMTP server RSA certificate file
       specified with $smtpd_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

smtpd_tls_loglevel (default: 0)
       Enable additional Postfix SMTP server logging of TLS activity.  Each
       logging level also includes the information that is logged at a lower
       logging level.


              0 Disable logging of TLS activity.


              1 Log TLS handshake and certificate information.


              2 Log levels during TLS negotiation.


              3 Log hexadecimal and ASCII dump of TLS negotiation process.


              4 Also log hexadecimal and ASCII dump of complete transmission
              after STARTTLS.

       Use "smtpd_tls_loglevel = 3" only in case of problems. Use of loglevel
       4 is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP server will use with
       mandatory TLS encryption. The default grade ("medium") is sufficiently
       strong that any benefit from globally restricting TLS sessions to a
       more stringent grade is likely negligible, especially given the fact
       that many implementations still do not offer any stronger ("high"
       grade) ciphers, while those that do, will always use "high" grade
       ciphers. So insisting on "high" grade ciphers is generally counter-
       productive. Allowing "export" or "low" ciphers is typically not a good
       idea, as systems limited to just these are limited to obsolete
       browsers. No known SMTP clients fail to support at least one "medium"
       or "high" grade cipher.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or stronger OpenSSL ciphers.  This is the
              most appropriate setting for public MX hosts, and is always used
              with opportunistic TLS encryption. The underlying cipherlist is
              specified via the tls_export_cipherlist configuration parameter,
              which you are strongly encouraged to not change.

       low    Enable "LOW" grade or stronger OpenSSL ciphers. The underlying
              cipherlist is specified via the tls_low_cipherlist configuration
              parameter, which you are strongly encouraged to not change.

       medium Enable "MEDIUM" grade or stronger OpenSSL ciphers. These use
              128-bit or longer symmetric bulk-encryption keys. This is the
              default minimum strength for mandatory TLS encryption. The
              underlying cipherlist is specified via the tls_medium_cipherlist
              configuration parameter, which you are strongly encouraged to
              not change.

       high   Enable only "HIGH" grade OpenSSL ciphers. The underlying
              cipherlist is specified via the tls_high_cipherlist
              configuration parameter, which you are strongly encouraged to
              not change.

       null   Enable only the "NULL" OpenSSL ciphers, these provide
              authentication without encryption.  This setting is only
              appropriate in the rare case that all clients are prepared to
              use NULL ciphers (not normally enabled in TLS clients). The
              underlying cipherlist is specified via the tls_null_cipherlist
              configuration parameter, which you are strongly encouraged to
              not change.

       Cipher types listed in smtpd_tls_mandatory_exclude_ciphers or
       smtpd_tls_exclude_ciphers are excluded from the base definition of the
       selected cipher grade. See smtpd_tls_ciphers for cipher controls that
       apply to opportunistic TLS.

       The underlying cipherlists for grades other than "null" include
       anonymous ciphers, but these are automatically filtered out if the
       server is configured to ask for client certificates.  You are very
       unlikely to need to take any steps to exclude anonymous ciphers, they
       are excluded automatically as required.  If you must exclude anonymous
       ciphers even when Postfix does not need or use peer certificates, set
       "smtpd_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only
       when TLS is enforced, set "smtpd_tls_mandatory_exclude_ciphers =
       aNULL".

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_exclude_ciphers (default: empty)
       Additional list of ciphers or cipher types to exclude from the SMTP
       server cipher list at mandatory TLS security levels. This list works in
       addition to the exclusions listed with smtpd_tls_exclude_ciphers (see
       there for syntax details).

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_protocols (default: !SSLv2)
       The SSL/TLS protocols accepted by the Postfix SMTP server with
       mandatory TLS encryption. If the list is empty, the server supports all
       available SSL/TLS protocol versions.  A non-empty value is a list of
       protocol names separated by whitespace, commas or colons. The supported
       protocol names are "SSLv2", "SSLv3" and "TLSv1", and are not case
       sensitive.

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". If an older Postfix version is linked against OpenSSL 1.0.1
       or later, these, or any other new protocol versions, are
       unconditionally enabled.

       With Postfix >= 2.5 the parameter syntax is expanded to support
       protocol exclusions. One can now explicitly exclude SSLv2 by setting
       "smtpd_tls_mandatory_protocols = !SSLv2". To exclude both SSLv2 and
       SSLv3 set "smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing the
       protocols to include, rather than protocols to exclude, is supported,
       but not recommended. The exclusion form more closely matches the
       behaviour when the OpenSSL library is newer than Postfix.

       Since SSL version 2 has known protocol weaknesses and is now
       deprecated, the default setting excludes "SSLv2".  This means that by
       default, SSL version 2 will not be used at the "encrypt" security
       level.

       Example:

       smtpd_tls_mandatory_protocols = TLSv1
       # Alternative form with Postfix >= 2.5:
       smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.3 and later.

smtpd_tls_protocols (default: empty)
       List of TLS protocols that the Postfix SMTP server will exclude or
       include with opportunistic TLS encryption. This parameter SHOULD be
       left at its default empty value, allowing all protocols to be used with
       opportunistic TLS.

       In main.cf the values are separated by whitespace, commas or colons. An
       empty value means allow all protocols. The valid protocol names, (see
       \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1". In
       smtp_tls_policy_maps table entries, "protocols" attribute values are
       separated by a colon.

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". If an older Postfix version is linked against OpenSSL 1.0.1
       or later, these, or any other new protocol versions, are
       unconditionally enabled.

       To include a protocol list its name, to exclude it, prefix the name
       with a "!" character. To exclude SSLv2 even for opportunistic TLS set
       "smtpd_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
       "smtpd_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the
       protocols to include, rather than protocols to exclude, is supported,
       but not recommended.  The exclusion form more closely matches the
       behaviour when the OpenSSL library is newer than Postfix.

       Example:
       smtpd_tls_protocols = !SSLv2

       This feature is available in Postfix 2.6 and later.

smtpd_tls_received_header (default: no)
       Request that the Postfix SMTP server produces Received:  message
       headers that include information about the protocol and cipher used, as
       well as the client CommonName and client certificate issuer CommonName.
       This is disabled by default, as the information may be modified in
       transit through other mail servers.  Only information that was recorded
       by the final destination can be trusted.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_req_ccert (default: no)
       With mandatory TLS encryption, require a trusted remote SMTP client
       certificate in order to allow TLS connections to proceed.  This option
       implies "smtpd_tls_ask_ccert = yes".

       When TLS encryption is optional, this setting is ignored with a warning
       written to the mail log.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_security_level (default: empty