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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 log-
              ical 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 configu-
       ration 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  configura-
       tion  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_reject_code (default: 554)
       The  numerical  Postfix  SMTP  server  response  code  when a client is
       rejected by an access(5) map restriction.

       Do not change this unless you have a complete understanding of RFC 821.

address_verify_default_transport (default: $default_transport)
       Overrides the default_transport parameter setting for address verifica-
       tion 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 verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_map (default: empty)
       Optional lookup table for persistent address verification status  stor-
       age.   The  table is maintained by the verify(8) service, and is opened
       before the process releases privileges.

       By default, the information is kept in volatile  memory,  and  is  lost
       after "postfix reload" or "postfix stop".

       Specify a location in a file system that will not fill up. If the data-
       base becomes corrupted, the world comes to an end.  To  recover  delete
       the file and do "postfix reload".

       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_direc-
       tory, and a warning is logged.

       Examples:

       address_verify_map = hash:/var/lib/postfix/verify
       address_verify_map = btree:/var/lib/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  verifica-
       tion 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: 3)
       How many times to query the verify(8) service for the completion of  an
       address verification request in progress.

       The default poll count is 3.

       Specify  1  to  implement  a crude form of greylisting, that is, always
       defer the first delivery request for a never seen before address.

       Example:

       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 veri-
       fication 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  verifica-
       tion 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_relayhost_maps    (default:     $sender_depen-
       dent_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 verifica-
       tion 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, respec-
       tively.

       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  ter-
       minator  into  the  command  line, this is difficult to enforce consis-
       tently and globally.

       As of Postfix version 2.5, this feature is implemented  by  trivial-re-
       write(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 hap-
       pens 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-speci-
       fied  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 direc-
       tory,  and is used by set-gid Postfix commands such as postqueue(1) and
       postdrop(1).

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 for mail
       that Postfix forwards internally, nor for mail that  Postfix  generates
       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, infor-
       mation 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 hap-
       pens 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 spec-
       ify full domain names instead.

       Note 2: with Postfix version 2.2, message header address rewriting hap-
       pens 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 pass-
       word 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).   Con-
       tinue  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 pass-
       word 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).   Con-
       tinue  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).  Con-
       tinue 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  com-
       mand 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  ver-
       sion  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  Post-
       fix versions before 2.0. The current and more extensible "name = value"
       format is needed in order to implement more  sophisticated  functional-
       ity.

       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,    $vir-
       tual_alias_domains, or $virtual_mailbox_domains.  By default, the Post-
       fix 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.  If you increase this
       limit, then you should increase the  mime_nesting_limit  value  propor-
       tionally.

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 con-
       figuration 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 First-
       name.Lastname.   The table format and lookups are documented in canoni-
       cal(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_expan-
       sion_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 com-
              mands).

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

       With Postfix command that run with set-gid privileges, a  config_direc-
       tory  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 main-
       tains a limited pool of cached sessions.

connection_cache_status_update_time (default: 600s)
       How  frequently the scache(8) server logs usage statistics with connec-
       tion 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)
       The  name  of  a  mail delivery transport that filters mail after it is
       queued.

       This parameter uses the same syntax as the right-hand side of a Postfix
       transport(5)  table. This setting has a lower precedence than a content
       filter  that  is  specified  with  an   access(5)   table   or   in   a
       header_checks(5) or body_checks(5) table.

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   par-
       ent_domain_matches_subdomains parameter.

       Examples:

       debug_peer_list = 127.0.0.1
       debug_peer_list = some.domain

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 max-
       imum, 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  over-
       ride,  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  set-
       tings.

       This  parameter speeds up the moment when a message preemption can hap-
       pen. Instead of  waiting  until  the  full  amount  of  delivery  slots
       required  is available, the preemption can happen when transport_deliv-
       ery_slot_discount percent of the required amount plus  transport_deliv-
       ery_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 hap-
       pen. Instead of  waiting  until  the  full  amount  of  delivery  slots
       required  is available, the preemption can happen when transport_deliv-
       ery_slot_discount percent of the required amount plus  transport_deliv-
       ery_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 over-
       ride, 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 desti-
       nation's pseudo-cohort failure count is reset each time a delivery com-
       pletes without connection or handshake failure for that specific desti-
       nation.

       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 com-
       patible with earlier Postfix versions.

default_destination_concurrency_limit (default: 20)
       The default maximal number of parallel deliveries to the same  destina-
       tion.  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-spe-
       cific 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 feed-
       back, 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    $trans-
       port_destination_concurrency_failed_cohort_limit).  To make the  sched-
       uler  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  inclu-
              sive.   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  com-
       patible 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  inclu-
              sive. The default setting of "1" is compatible with Postfix ver-
              sions 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 deliv-
       eries 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.

       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  cor-
       responding  per-destination  concurrency  limit  from  concurrency  per
       domain into concurrency per recipient.

       Use transport_destination_recipient_limit to specify  a  transport-spe-
       cific  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 num-
       ber  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_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 deliv-
       ery 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 numeri-
              cal SMTP response code is required, and must appear at the start
              of  the  reply. With Postfix version 2.3 and later this informa-
              tion 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 tem-
       plate, 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 recip-
       ients.  These limits take priority over the global qmgr_message_recipi-
       ent_limit  after the message has been assigned to the respective trans-
       ports.  See also default_extra_recipient_limit and qmgr_message_recipi-
       ent_minimum.

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

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 load-
       ing  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 deliv-
       eries.

       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 desti-
       nations   that   do   not   match   $mydestination,   $inet_interfaces,
       $proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains, or
       $relay_domains.   In order of decreasing precedence, the nexthop desti-
       nation  is  taken  from  $default_transport,   $sender_dependent_relay-
       host_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
       part is optional.  For more details see the transport(5) manual page.

       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 821.

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 TLS

       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  mail-
       box 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-Trans-
       fer-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  dis-
       abled,  hosts  are looked up with the getaddrinfo() system library rou-
       tine 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  spe-
       cial  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  har-
       vest email addresses.

       Example:

       disable_vrfy_command = no

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_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  ver-
       sions,  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-stan-
       dard  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, rewrit-
       ten  recipient),  and generates non-empty original recipient queue file
       records.

       When this parameter is set to no, the cleanup(8) daemon performs dupli-
       cate 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  ver-
       sion 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 white-
       space 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, Post-
       fix 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 pass-
       word 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_direc-
       tory, 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_direc-
       tory, 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  destina-
       tions  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:ta-
       ble" 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 let-
       ter 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 let-
       ter 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-destina-
       tion  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, exe-
       cute the command "postfix reload".

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

       Before  Postfix version 2.2, the default list of hashed queues was sig-
       nificantly 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, exe-
       cute 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  mes-
       sage 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_direc-
       tory, 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,  config-
       ure 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 Post-
       fix 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  white-
       space  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 mas-
       ter.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 use-
       ful with virtual hosting of domains on  secondary  IP  addresses,  when
       each IP address serves a different domain (and has a different $myhost-
       name 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",  sepa-
       rated  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 des-
       tination 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 821.

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  situa-
       tions.  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_bind_address (default: empty)
       The LMTP-specific version of the smtp_bind_address configuration param-
       eter.  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_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.

       The effectiveness of cached connections will be determined by the  num-
       ber 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 spec-
              ified 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  con-
              figuration 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  con-
       figuration 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  con-
       figuration 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 con-
       figuration 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  con-
       figuration 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 con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_destination_concurrency_limit   (default:    $default_destination_concur-
       rency_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_recipi-
       ent_limit)
       The  maximal  number  of  recipients  per delivery 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.

       Setting this parameter to a value of 1 changes the meaning of lmtp_des-
       tination_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_key-
       word_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  dis-
              card LHLO keywords selectively.

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

       This feature is available in Postfix 2.3 and later.

lmtp_host_lookup (default: dns)
       The LMTP-specific version of the smtp_host_lookup configuration parame-
       ter.  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_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_pix_workaround_delay_time (default: 10s)
       The LMTP-specific version of the smtp_pix_workaround_delay_time config-
       uration 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  configura-
       tion 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_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  configura-
       tion 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 configura-
       tion 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  configura-
       tion 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 configura-
       tion 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-dic-
              tionary 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 config-
       uration 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_secu-
       rity_options)
       The   LMTP-specific   version   of   the   smtp_sasl_tls_verified_secu-
       rity_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  parame-
       ter.  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 parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 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_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_enforce_peername (default: yes)
       The  LMTP-specific  version of the smtp_tls_enforce_peername configura-
       tion 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 con-
       figuration 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 configura-
       tion 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 param-
       eter.  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 param-
       eter.  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 configura-
       tion 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: SSLv3, TLSv1)
       The  LMTP-specific version of the smtp_tls_mandatory_protocols configu-
       ration 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  configu-
       ration 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 param-
       eter.  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_scert_verifydepth (default: 9)
       The  LMTP-specific version of the smtp_tls_scert_verifydepth configura-
       tion 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  configura-
       tion 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  con-
       figuration 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 config-
       uration 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  configura-
       tion 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 /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_destination_concurrency_limit (default: 2)
       The  maximal  number of parallel deliveries via the local mail delivery
       transport  to  the  same  recipient  (when   "local_destination_recipi-
       ent_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_des-
       tination_concurrency_limit from concurrency per recipient into  concur-
       rency 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 re-
       write 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 suit-
              able 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 rewrit-
       ing when mail from a remote client is forwarded by a  neighboring  sys-
       tem.

           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 recip-
       ient  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,  spec-
       ify "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_recipi-
       ent_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  "fall-
              back_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] des-
       tinations  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
       part is optional.  For more details see the transport(5) manual page.

       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  $mydestina-
       tion,  $inet_interfaces  or $proxy_interfaces is returned as undeliver-
       able.

       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  pro-
       cesses  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.  Post-
       fix 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 pri-
       mary group ID privileges of the recipient.  Exception: command delivery
       for  root executes with $default_privs privileges.  This is not a prob-
       lem, 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  ver-
              sion 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_direc-
       tory, 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_direc-
       tory, 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_direc-
       tory, 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_direc-
       tory, 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_sender   or  reject_rhsbl_recipient
       restriction.

       Do not change this unless you have a complete understanding of RFC 821.

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.exam-
       ple.com", but strips "userATany.com"  to  "user@exam-
       ple.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  mas-
       querading, 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).  Con-
       tinue 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

max_idle (default: 100s)
       The maximum amount of time that an idle Postfix  daemon  process  waits
       for an incoming connection before terminating voluntarily.  This param-
       eter 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 $mini-
       mal_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 undeliv-
       erable.

       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.

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 -n 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 -n 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  unavail-
       able 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.

       This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -n 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 -n 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_helo_macros (default: see postconf -n 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  mean-
       ings.

       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 MIL-
       TER_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 -n 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: 2)
       The mail filter protocol version and optional protocol  extensions  for
       communication  with  a  Milter (mail filter) application. Postfix sends
       this version number during the initial protocol handshake.   It  should
       match  the  version number that is expected by the mail filter applica-
       tion (or by its Milter library).

       Protocol versions:

       2      Use Sendmail 8 mail filter protocol version  2  (default  as  of
              Sendmail version 8.11).

       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 as of
              Sendmail version 8.14).

       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 -n 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 -n 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 proces-
       sor is unable to distinguish between boundary strings that do not  dif-
       fer 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.  Post-
       fix 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_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 restric-
       tion.

       Do not change this unless you have a complete understanding of RFC 821.

       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_recipi-
       ent_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).  Con-
       tinue 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.  $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
       name  from  gethostname(),  which  is  expected to be a fully-qualified
       domain name.  If it is only one component, then $mydomain  is  appended
       to it. $myhostname is used as a default value for many other configura-
       tion parameters.

       Example:

       myhostname = host.domain.tld

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 descrip-
       tion of the mynetworks_style parameter for more information.

       If  you specify the mynetworks list by hand, Postfix ignores the mynet-
       works_style setting.

       Specify a list of network addresses or network/netmask patterns,  sepa-
       rated  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 ade-
       quate 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 head-
       ers  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  adminis-
       trator'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:  post-
              master).

       2bounce
              Send undeliverable bounced mail to the postmaster. The notifica-
              tion   is   sent   to   the   address   specified    with    the
              2bounce_notice_recipient configuration parameter (default: post-
              master).

       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:  post-
              master).

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

       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 configura-
              tion 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.

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.

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@domain -&gt; joe.user", the
       address "joe+foo@domain" would rewrite to "joe.user+foo".

       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.

qmgr_clog_warn_time (default: 300s)
       The minimal delay between warnings that a specific destination is clog-
       ging 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_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_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 host-
       name 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 sec-
       onds 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 version 2.1 SMTP server rejects MAIL FROM com-
       mands  when  the  amount  of  free  space  is   less   than   1.5*$mes-
       sage_size_limit.  To specify a higher minimum free space limit, specify
       a queue_minfree value that is at least 1.5*$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_back-
       off_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 parame-
       ter. 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,  con-
       figure 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  com-
       mand-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  con-
              tent 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  sup-
       ported) 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 recipi-
              ent 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 for mail
       that  Postfix  forwards internally, nor for mail that Postfix generates
       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  recipi-
       ent  addresses.  The table format and lookups are documented in canoni-
       cal(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 821.

relay_clientcerts (default: empty)
       List  of  tables  with  remote SMTP client-certificate fingerprints for
       which  the  Postfix  SMTP  server  will  allow  access  with  the  per-
       mit_tls_clientcerts  feature.  The fingerprint digest algorithm is con-
       figurable 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  RESTRIC-
       TION_CLASS_README.

       This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit   (default:   $default_destination_concur-
       rency_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_recipi-
       ent_limit)
       The  maximal  number  of  recipients per delivery 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.

       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  par-
       ent_domain_matches_subdomains parameter.  For  details  about  how  the
       relay_domains   value   is  used,  see  the  description  of  the  per-
       mit_auth_destination  and  reject_unauth_destination   SMTP   recipient
       restrictions.

       Domains  that match $relay_domains are delivered with the $relay_trans-
       port mail delivery  transport.  The  SMTP  server  validates  recipient
       addresses  with  $relay_recipient_maps and rejects non-existent recipi-
       ents.   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  per-
       mit_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 821.

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 inno-
       cent 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
       part is optional.  For more details see the transport(5) manual page.

       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_trans-
       port, default_transport, sender_dependent_relayhost_maps and  with  the
       transport(5) table.

       On  an intranet, specify the organizational domain name. If your inter-
       nal 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  [host-
       name] turns off MX lookups.

       If  you're  connected  via  UUCP,  see  the UUCP_README file for useful
       information.

       Examples:

       relayhost = $mydomain
       relayhost = [gateway.my.domain]
       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 docu-
       mented 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_re-
       write_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)
       Whether or not a local(8) recipient's home directory must exist  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 (NOT RECOMMENDED).

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 incor-
       rect.

       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  re-
       write 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.

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_depen-
       dent_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 for mail
       that Postfix forwards internally, nor for mail that  Postfix  generates
       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  enve-
       lope 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  canoni-
       cal(5).

       Example:  you  want to rewrite the SENDER address "userATugly.domain" to
       "userATpretty.domain", while still being able to send mail to the RECIP-
       IENT address "userATugly.domain".

       Note: $sender_canonical_maps is processed before $canonical_maps.

       Example:

       sender_canonical_maps = hash:/etc/postfix/sender_canonical

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.
       This  information  is overruled with relay_transport, 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 sta-
       tus reports.

       This feature is available in Postfix 2.0 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 exam-
       ple:

           /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 exam-
       ple:

           /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  deci-
       sions,  or TLS certificate verification. The value "no" hardens Postfix
       smtp_tls_per_site hostname-based policies against false hostname infor-
       mation  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 destina-
       tions.  With SMTP connection caching, a connection is not closed  imme-
       diately  after  completion of a mail transaction.  Instead, the connec-
       tion 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_con-
       nection_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  dis-
       tribution 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_concur-
       rency_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_recipi-
       ent_limit)
       The  maximal  number  of  recipients  per delivery 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.

       Setting this parameter to a value of 1 changes the meaning of smtp_des-
       tination_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 ta-
       ble  is  not  indexed  by  hostname  for  consistency  with  smtpd_dis-
       card_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  dis-
              card EHLO keywords selectively.

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 cer-
       tificate, 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  Com-
       monName   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, Post-
       fix 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 (and DSN 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  when the Postfix SMTP client uses to look up a host's
       IP address.  This parameter is ignored when DNS lookups are disabled.

       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 ver-
       sion 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  send-
       ing large messages over slow network connections.

smtp_pix_workaround_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with per-des-
       tination workarounds for CISCO PIX firewall bugs.   The  table  is  not
       indexed   by   hostname  for  consistency  with  smtp_discard_ehlo_key-
       word_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 insensi-
       tive.  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_work-
              around_delay_time and smtp_pix_workaround_threshold_time parame-
              ter 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  set-
       tings 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 821. This includes putting quotes around an address localpart  that
       ends in ".".

       The  default  is  to comply with RFC 821. 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_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  authen-
       tication  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_concur-
       rency_limit = 1", etc.), otherwise multiple delivery agents may experi-
       ence 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  pass-
       words, and requires that Postfix is compiled with TLS support.

       Example:

       smtp_sasl_auth_cache_name = proxy:btree:/var/lib/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  unde-
       liverable.  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 implemen-
       tations  may support different mechanism lists. By default, the Postfix
       SMTP client will use the  intersection  of  the  two.  smtp_sasl_mecha-
       nism_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_secu-
       rity_options)
       The SASL authentication security options that the Postfix  SMTP  client
       uses  for  TLS  encrypted SMTP sessions with a verified server certifi-
       cate. This feature is under construction as of Postfix version 2.3.

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  connec-
       tion  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  immedi-
       ately.

       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)
       The  file with the certificate of the certification authority (CA) that
       issued the Postfix SMTP client certificate.  This is needed  only  when
       the  CA  certificate  is  not already present in the client certificate
       file.

       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.

       Example:

       smtp_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

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  usu-
       ally  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_dcert_file =
           smtp_tls_key_file =
           smtp_tls_dkey_file =

       The best way to use the default settings is to comment  out  the  above
       parameters in main.cf if present.

       In  order to verify certificates, the CA certificate (in case of a cer-
       tificate chain, all CA certificates) must be available.  You should add
       these  certificates  to  the client certificate, the client certificate
       first, then the issuing CA(s).

       Example: the certificate for "client.dom.ain" was issued by "intermedi-
       ate  CA"  which  itself  has  a  certificate  of "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 also 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 or smtp_tls_dcert_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_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, but file permissions should grant  read/write  access
       only to the system superuser account ("root").

       This feature is available in Postfix 2.2 and 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  environ-
       ment 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 dis-
       ables 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 = finger-
       print). At this security level, certificate authorities are  not  used,
       and  certificate expiration times are ignored. Instead, server certifi-
       cates 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  fin-
       gerprints  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 destina-
       tions.  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  cer-
       tificate   fingerprints.   At  the  "fingerprint"  TLS  security  level
       (smtp_tls_security_level = fingerprint), the server certificate is ver-
       ified by directly matching its fingerprint. The fingerprint is the mes-
       sage 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 func-
       tion 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, but file permissions should grant read/write access
       only to the system superuser account ("root").

       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 crypt-analytic 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 the mainstream "EXPORT" grade or better OpenSSL  ciphers.
              This is always used for opportunistic encryption. It is not rec-
              ommended 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. The default value of
              tls_export_cipherlist includes anonymous ciphers, but these  are
              automatically filtered out if the client is configured to verify
              server certificates. If you must exclude anonymous ciphers  also
              at   the   "encrypt"   security   level,   set  "smtp_tls_manda-
              tory_exclude_ciphers = aNULL".

       low    Enable the mainstream "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. The default  value  of  tls_low_cipherlist  includes
              anonymous  ciphers,  but these are automatically filtered out if
              the client is configured to verify server certificates.  If  you
              must  exclude  anonymous  ciphers also at the "encrypt" security
              level, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

       medium Enable the mainstream "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.   The  default  value  of
              tls_medium_cipherlist includes anonymous ciphers, but these  are
              automatically filtered out if the client is configured to verify
              server certificates. If you must exclude anonymous ciphers  also
              at   the   "encrypt"   security   level,   set  "smtp_tls_manda-
              tory_exclude_ciphers = aNULL".

       high   Enable only the mainstream "HIGH" grade OpenSSL  ciphers.   This
              setting  is appropriate when all mandatory TLS destinations sup-
              port some of "HIGH" grade ciphers, this  is  not  uncommon.  The
              underlying  cipherlist  is specified via the tls_high_cipherlist
              configuration parameter, which you are  strongly  encouraged  to
              not  change.  The  default value of tls_high_cipherlist includes
              anonymous ciphers, but these are automatically filtered  out  if
              the  client  is configured to verify server certificates. If you
              must exclude anonymous ciphers also at  the  "encrypt"  security
              level, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

       null   Enable  only the "NULL" OpenSSL ciphers, these provide authenti-
              cation 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 config-
              ured 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  default
              value of tls_null_cipherlist excludes anonymous ciphers (OpenSSL
              0.9.8 has NULL ciphers that offer data integrity without encryp-
              tion or authentication).

       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).

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: SSLv3, TLSv1)
       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  \fBfB-
       SSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

       With  Postfix >= 2.5 the parameter syntax is expanded to support proto-
       col 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 still sup-
       ported; use the form you find more intuitive.

       Since SSL version 2 has known protocol weaknesses  and  is  now  depre-
       cated,  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:

       smtp_tls_mandatory_protocols = TLSv1
       # Alternative form with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3

       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 discour-
       aged. 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) ta-
       ble, 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 over-
              rides    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 spe-
              cific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peer-
              name = 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  spe-
              cific  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  cer-
              tificate,  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_peer-
              name settings.

       The above keywords correspond to the "none", "may", "encrypt" and "ver-
       ify"  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 only apply when TLS  encryption
       is  mandatory.  Connections for which encryption is optional enable all
       "export" grade and better ciphers.

       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 cer-
       tificate, 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  increas-
       ing security are:

       none   No TLS. No additional attributes are supported at this level.

       may    Opportunistic  TLS.  No  additional  attributes are supported at
              this level. Since sending in the clear is acceptable,  demanding
              stronger  than  default  TLS  security parameters merely reduces
              inter-operability.    Postfix   2.3   and   later   ignore   the
              smtp_tls_mandatory_ciphers    and   smtp_tls_mandatory_protocols
              parameters at this security level; all protocols are allowed and
              "export"  grade or better ciphers are used.  When TLS handshakes
              fail, the connection is retried with TLS disabled.  This  allows
              mail  delivery  to  sites with non-interoperable TLS implementa-
              tions.

       encrypt
              Mandatory TLS encryption. At this level and higher the  optional
              "ciphers"   attribute   overrides  the  main.cf  smtp_tls_manda-
              tory_ciphers parameter  and  the  optional  "protocols"  keyword
              overrides  the  main.cf  smtp_tls_mandatory_protocols parameter.
              In the policy table, multiple protocols  must  be  separated  by
              colons,  as  attribute values may not contain whitespace or com-
              mas.

       fingerprint
              Certificate fingerprint verification. Available with Postfix 2.5
              and later. At this security level, there are no trusted certifi-
              cate 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 finger-
              prints 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  parame-
              ter. 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 ta-
       ble 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_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 compati-
       bility 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 exam-
       ple, 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_pol-
       icy_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. TLS will be used if supported by the server.
              Since sending in the clear  is  acceptable,  demanding  stronger
              than  default TLS security parameters merely reduces inter-oper-
              ability.  Postfix  2.3  and  later  ignore  the  smtp_tls_manda-
              tory_ciphers and smtp_tls_mandatory_protocols parameters at this
              security level; all protocols are allowed and "export" grade  or
              better  ciphers are used.  When TLS handshakes fail, the connec-
              tion 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 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 certifi-
              cate authorities. The certificate trust chain, expiration  date,
              ...    are    not   checked.   Instead,   the   smtp_tls_finger-
              print_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 appropri-
              ate 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 param-
              eter. The default matching rule is  that  a  server  certificate
              matches when its name is equal to or is a sub-domain of the nex-
              thop 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

       # 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 ses-
       sion 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_data-
       base,  $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 data-
       base.

       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_direc-
       tory, and a warning is logged.

       Example:

       smtp_tls_session_cache_database = btree:/var/lib/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 informa-
       tion.  A cache cleanup is performed periodically  every  $smtp_tls_ses-
       sion_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_pol-
       icy_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 distinc-
              tions 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 strat-
              egy  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 ver-
              ification  strategy  of  the  "MUST"  keyword  in  the  obsolete
              smtp_tls_per_site  table, and is suitable for use with the "ver-
              ify" 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  START-
       TLS  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  com-
       mand 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. Typ-
       ical 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 com-
       mand 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,  Post-
       fix 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 connection count, connection rate, or
       SMTP request rate restrictions. See the mynetworks  parameter  descrip-
       tion 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  speci-
       fied 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  host-
       name 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  Post-
       fix actually accepts those recipients.  The time unit is specified with
       the anvil_rate_time_unit configuration parameter.

       By default, a client can make 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.

       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 restric-
       tion 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 success-
              fully.  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.

       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 net-
              work 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  spe-
              cial  CA  issues  the certificates and only this CA is listed as
              trusted CA, otherwise all clients with a recognized  certificate
              would  be allowed to relay. This feature is available with Post-
              fix version 2.2.

       permit_tls_clientcerts
              Permit the request when the remote SMTP client certificate  fin-
              gerprint  is  listed  in  $relay_clientcerts.   The  fingerprint
              digest  algorithm  is  configurable  via  the  smtpd_tls_finger-
              print_digest  parameter (hard-coded as md5 prior to Postfix ver-
              sion 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).  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.

       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).   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.

       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 Post-
              fix 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 ear-
              lier 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  fea-
              ture 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 com-
              mands.
              The plaintext_reject_code parameter specifies the response  code
              for  rejected  requests (default:  450).  This feature is avail-
              able 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 com-
              mands ahead of time without knowing that Postfix  actually  sup-
              ports  ESMTP  command pipelining. This stops mail from bulk mail
              software that improperly uses ESMTP command pipelining in  order
              to speed up deliveries.
              Note:    reject_unauth_pipelining    is   not   useful   outside
              smtpd_data_restrictions when 1)  the  client  uses  ESMTP  (EHLO
              instead  of  HELO)  and  2) with "smtpd_delay_reject = yes" (the
              default).  The use  of  reject_unauth_pipelining  in  the  other
              restriction contexts is therefore not recommended.

       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
              to 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_restric-
              tions, 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_data_restrictions (default: empty)
       Optional access restrictions that the Postfix SMTP  server  applies  in
       the context of the SMTP DATA command.

       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 restric-
       tion that matches wins.

       The following restrictions are valid in this context:

       o      Generic restrictions that can be used in any SMTP  command  con-
              text, 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.

       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_restric-
       tions, $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 dis-
              card 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.

       This feature is available in Postfix 2.2 and later.

       See smtpd_data_restrictions for syntax details.

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.

       The Postfix ETRN implementation accepts only destinations that are eli-
       gible  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  restric-
       tion 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 con-
              text, 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  causes 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: 20)
       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.

smtpd_helo_required (default: no)
       Require that a remote SMTP client introduces itself at the beginning of
       an SMTP session with the HELO or EHLO command.

       Example:

       smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the  con-
       text of the SMTP HELO command.

       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 restric-
       tion 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.

       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:  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_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:  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_invalid_helo_hostname  (with Postfix < 2.3: reject_invalid_host-
       name)
              Reject the request when the HELO  or  EHLO  hostname  syntax  is
              invalid.
              The  invalid_hostname_reject_code specifies the response code to
              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.
              The non_fqdn_reject_code parameter specifies the  response  code
              to 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).  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.
              This feature is available in Postfix 2.0 and later.

       reject_unknown_helo_hostname  (with Postfix < 2.3: reject_unknown_host-
       name)
              Reject the request when the HELO or EHLO hostname has no  DNS  A
              or MX record.
              The  unknown_hostname_reject_code specifies the response code to
              rejected requests (default: 450).

       Other restrictions that are valid in this context:

       o      Generic restrictions that can be used in any SMTP  command  con-
              text, 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: 100)
       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.

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 dis-
       abled.  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  dele-
       gated 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_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_desti-
       nation)
       The access restrictions that the Postfix SMTP  server  applies  in  the
       context of the RCPT TO command.

       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@else-
              where@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 restric-
       tion 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 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_recipient_ns_access type:table
              Search  the specified access(5) database for the DNS servers for
              the RCPT TO  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.

       permit_auth_destination
              Permit the request when one of the following is true:

       o      Postfix  is mail forwarder: the resolved RCPT TO address 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 address
              matches  $mydestination,  $inet_interfaces,   $proxy_interfaces,
              $virtual_alias_domains,  or  $virtual_mailbox_domains,  and  the
              address  contains  no   sender-specified   routing   (user@else-
              where@domain).

       permit_mx_backup
              Permit  the  request when the local mail system is backup MX for
              the RCPT TO address, or when the address is an authorized desti-
              nation (see permit_auth_destination for definition).

       o      Safety:  permit_mx_backup  does  not  accept addresses that have
              sender-specified  routing   information   (example:   user@else-
              where@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 per-
              mit_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
              to 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).   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 address 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 address
              matches  $mydestination,  $inet_interfaces,   $proxy_interfaces,
              $virtual_alias_domains,  or  $virtual_mailbox_domains,  and con-
              tains 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 address, and the RCPT TO 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 response
              code  for  rejected  requests  (default:  450).  The response is
              always 450 in case of a temporary DNS error.

       reject_unlisted_recipient  (with  Postfix  version  2.0:  check_recipi-
       ent_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 reach-
              able.  Address verification information is managed by  the  ver-
              ify(8)  server;  see  the  ADDRESS_VERIFICATION_README  file for
              details.
              The  unverified_recipient_reject_code  parameter  specifies  the
              response  when  an  address  is  known  to bounce (default: 450,
              change into 550 when you are confident that it  is  safe  to  do
              so).  Postfix  replies with 450 when an address probe failed due
              to a temporary problem.  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 con-
              text, 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_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.

       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 $vir-
              tual_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 restric-
       tion is specified. This can slow down an explosion of forged mail  from
       worms or viruses.

       o      The  sender  domain  matches $mydestination, $inet_interfaces or
              $proxy_interfaces, but the sender is not listed in $local_recip-
              ient_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  $vir-
              tual_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  mes-
       sage 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,  $mynet-
       works 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 net-
       work 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_inter-
              faces 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  con-
       text of the MAIL FROM command.

       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 restric-
       tion 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
              to 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).  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  unau-
              thenticated  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 response
              code for rejected requests  (default:  450).   The  response  is
              always 450 in case of a temporary DNS error.

       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 reach-
              able.  Address verification information is managed by  the  ver-
              ify(8)  server;  see  the  ADDRESS_VERIFICATION_README  file for
              details.
              The  unverified_sender_reject_code   parameter   specifies   the
              response  when  an  address  is  known  to bounce (default: 450,
              change into 550 when you are confident that it  is  safe  to  do
              so).  Postfix  replies with 450 when an address probe failed due
              to a temporary problem.  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 con-
              text, 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_recipi-
              ent_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_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: 300s)
       The time limit for Postfix SMTP server write and read operations during
       TLS startup and shutdown handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: 300s)
       The time limit for sending a  Postfix  SMTP  server  response  and  for
       receiving a remote SMTP client request.

       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)
       The  file with the certificate of the certification authority (CA) that
       issued the Postfix SMTP server certificate.  This is needed  only  when
       the  CA  certificate  is  not already present in the server certificate
       file.  This file may also contain the CA certificates of other  trusted
       CAs.  You must use this file for the list of trusted CAs if you want to
       use chroot-mode.

       Example:

       smtpd_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)
       Directory with PEM format certificate authority certificates  that  the
       Postfix  SMTP  server  offers to remote SMTP clients for the purpose of
       client certificate verification.  Do not forget to create the necessary
       "hash"  links with, for example, "$OPENSSL_HOME/bin/c_rehash /etc/post-
       fix/certs".

       To use this option in chroot mode, this directory (or a copy)  must  be
       inside  the  chroot jail. Please note that in this case the CA certifi-
       cates are not offered to the client, so  that  e.g.   Netscape  clients
       might  not  offer  certificates issued by them.  Use of this feature is
       therefore not recommended.

       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 per-
       mit_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 mul-
       tiple 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 compati-
       bility 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 exam-
       ple, 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 simi-
       lar 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 cer-
       tificates, 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.

       In order to verify a certificate, the CA certificate (in case of a cer-
       tificate chain, all CA certificates) must be available.  You should add
       these certificates to the server certificate,  the  server  certificate
       first, then the issuing CA(s).

       Example: the certificate for "server.dom.ain" was issued by "intermedi-
       ate 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_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/ran-
       dom; on other system you may consider using the "Entropy Gathering Dae-
       mon 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  configu-
       ration 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, but file permissions should grant  read/write  access
       only to the system superuser account ("root").

       This feature is available in Postfix 2.2 and 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 essen-
       tial 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  encryp-
       tion  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  fin-
       gerprints   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 func-
       tion 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, but file permissions should grant read/write access
       only to the system superuser account ("root").

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.  Cipher  types  listed  in smtpd_tls_manda-
       tory_exclude_ciphers or smtpd_tls_exclude_ciphers are excluded from the
       base  definition  of  the selected cipher grade. With opportunistic TLS
       encryption, the "export" grade is used unconditionally with  exclusions
       specified only via smtpd_tls_exclude_ciphers.

       The following cipher grades are supported:

       export Enable  the mainstream "EXPORT" grade or better 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 configura-
              tion parameter, which you are strongly encouraged to not change.
              The default value of  tls_export_cipherlist  includes  anonymous
              ciphers,  but these are automatically filtered out if the server
              is configured to ask for client certificates. If you must always
              exclude  anonymous  ciphers,  set  "smtpd_tls_exclude_ciphers  =
              aNULL". To exclude anonymous ciphers only when TLS is  enforced,
              set "smtpd_tls_mandatory_exclude_ciphers = aNULL".

       low    Enable the mainstream "LOW" grade or better OpenSSL ciphers. The
              underlying cipherlist is specified  via  the  tls_low_cipherlist
              configuration  parameter,  which  you are strongly encouraged to
              not change. The default  value  of  tls_low_cipherlist  includes
              anonymous  ciphers,  but these are automatically filtered out if
              the server is configured to ask for client certificates. If  you
              must      always      exclude     anonymous     ciphers,     set
              "smtpd_tls_exclude_ciphers  =  aNULL".  To   exclude   anonymous
              ciphers   only  when  TLS  is  enforced,  set  "smtpd_tls_manda-
              tory_exclude_ciphers = aNULL".

       medium Enable the mainstream "MEDIUM" grade or better OpenSSL  ciphers.
              These  are  essentially the 128-bit or stronger ciphers. This is
              the default minimum strength for mandatory TLS encryption.  MSAs
              that  enforce  TLS  and  have  clients  that  do not support any
              "MEDIUM" or "HIGH" grade ciphers, may need to configure a weaker
              ("low"   or  "export")  minimum  cipher  grade.  The  underlying
              cipherlist is specified via the tls_medium_cipherlist configura-
              tion parameter, which you are strongly encouraged to not change.
              The default value of  tls_medium_cipherlist  includes  anonymous
              ciphers,  but these are automatically filtered out if the server
              is configured to ask for client certificates. If you must always
              exclude  anonymous  ciphers,  set  "smtpd_tls_exclude_ciphers  =
              aNULL". To exclude anonymous ciphers only when TLS is  enforced,
              set "smtpd_tls_mandatory_exclude_ciphers = aNULL".

       high   Enable  only  the  mainstream  "HIGH" grade OpenSSL ciphers. The
              underlying cipherlist is specified via  the  tls_high_cipherlist
              configuration  parameter,  which  you are strongly encouraged to
              not change. The default value  of  tls_high_cipherlist  includes
              anonymous  ciphers,  but these are automatically filtered out if
              the server is configured to ask for client certificates. If  you
              must      always      exclude     anonymous     ciphers,     set
              "smtpd_tls_exclude_ciphers  =  aNULL".  To   exclude   anonymous
              ciphers   only  when  TLS  is  enforced,  set  "smtpd_tls_manda-
              tory_exclude_ciphers = aNULL".

       null   Enable only the "NULL" OpenSSL ciphers, these provide  authenti-
              cation  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  parame-
              ter,  which  you  are  strongly  encouraged  to  not change. The
              default value of tls_null_cipherlist excludes anonymous  ciphers
              (OpenSSL  0.9.8 has NULL ciphers that offer data integrity with-
              out encryption or authentication).

       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: SSLv3, TLSv1)
       The  SSL/TLS  protocols accepted by the Postfix SMTP server with manda-
       tory 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 sen-
       sitive.

       With Postfix >= 2.5 the parameter syntax is expanded to support  proto-
       col  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  still  sup-
       ported, use the form you find more intuitive.

       Since  SSL  version  2  has known protocol weaknesses and is now depre-
       cated, 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_received_header (default: no)
       Request that the Postfix SMTP server produces Received:  message  head-
       ers  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)
       The SMTP TLS security level for the Postfix SMTP server;  when  a  non-
       empty  value  is  specified,  this  overrides  the  obsolete parameters
       smtpd_use_tls and smtpd_enforce_tls. This  parameter  is  ignored  with
       "smtpd_tls_wrappermode = yes".

       Specify one of the following security levels:

       none   TLS will not be used.

       may    Opportunistic  TLS:  announce  STARTTLS support to SMTP clients,
              but do not require that clients use TLS encryption.

       encrypt
              Mandatory TLS encryption:  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-ref-
              erenced SMTP server. Instead, this option should be used only on
              dedicated servers.

       Note 1: the "fingerprint", "verify" and "secure" levels  are  not  sup-
       ported here.  The Postfix SMTP server logs a warning and uses "encrypt"
       instead.  To verify SMTP client certificates, see TLS_README for a dis-
       cussion  of  the  smtpd_tls_ask_ccert,  smtpd_tls_req_ccert,  and  per-
       mit_tls_clientcerts features.

       Note 2: The  parameter  setting  "smtpd_tls_security_level  =  encrypt"
       implies "smtpd_tls_auth_only = yes".

       Note  3:  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 2.3 and later.

smtpd_tls_session_cache_database (default: empty)
       Name  of  the file containing the optional Postfix SMTP server TLS ses-
       sion 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 smtpd(8) daemon does not use  this
       parameter  directly,  rather the cache is implemented indirectly in the
       tlsmgr(8) daemon. This means that  per-smtpd-instance  master.cf  over-
       rides of this parameter are not effective. Note, that each of the cache
       databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data-
       base,  $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 data-
       base.

       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_direc-
       tory, and a warning is logged.

       Example:

       smtpd_tls_session_cache_database = btree:/var/lib/postfix/smtpd_scache

       This feature is available in Postfix 2.2 and later.

smtpd_tls_session_cache_timeout (default: 3600s)
       The  expiration  time of Postfix SMTP server TLS session cache informa-
       tion. A cache cleanup is performed periodically  every  $smtpd_tls_ses-
       sion_cache_timeout  seconds. As with $smtpd_tls_session_cache_database,
       this parameter is implemented in the  tlsmgr(8)  daemon  and  therefore
       per-smtpd-instance master.cf overrides are not possible.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_wrappermode (default: no)
       Run the Postfix SMTP server in the non-standard "wrapper" mode, instead
       of using the STARTTLS command.

       If you want to support this service, enable  a  special  port  in  mas-
       ter.cf, and specify "-o smtpd_tls_wrappermode=yes" on the SMTP server's
       command line. Port 465 (smtps) was once chosen for this purpose.

       This feature is available in Postfix 2.2 and later.

smtpd_use_tls (default: no)
       Opportunistic TLS: announce STARTTLS support to SMTP  clients,  but  do
       not require that clients use TLS encryption.

       Note:  when invoked via "sendmail -bs", Postfix will never offer START-
       TLS 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.

soft_bounce (default: no)
       Safety net to keep mail queued that would otherwise be returned to  the
       sender.   This  parameter  disables locally-generated bounces, and pre-
       vents the Postfix SMTP  server  from  rejecting  mail  permanently,  by
       changing 5xx reply codes into 4xx.  However, soft_bounce is no cure for
       address rewriting mistakes or mail routing mistakes.

       Example:

       soft_bounce = yes

stale_lock_time (default: 500s)
       The time after which a stale exclusive  mailbox  lockfile  is  removed.
       This is used for delivery to file or mailbox.

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

stress (default: empty)
       This feature is documented in the STRESS_README document.

       This feature is available in Postfix 2.5 and later.

strict_7bit_headers (default: no)
       Reject mail with 8-bit text in message headers. This blocks  mail  from
       poorly written applications.

       This  feature  should  not be enabled on a general purpose mail server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime (default: no)
       Enable both strict_7bit_headers and strict_8bitmime_body.

       This feature should not be enabled on a general  purpose  mail  server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime_body (default: no)
       Reject  8-bit  message  body  text  without 8-bit MIME content encoding
       information.  This blocks mail from poorly written applications.

       Unfortunately, this also rejects majordomo approval requests  when  the
       included request contains valid 8-bit MIME mail, and it rejects bounces
       from mailers that do not MIME encapsulate 8-bit content  (for  example,
       bounces from qmail or from old versions of Postfix).

       This  feature  should  not be enabled on a general purpose mail server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_mailbox_ownership (default: yes)
       Defer delivery when a mailbox file is not owned by its recipient.   The
       default setting is not backwards compatible.

       This feature is available in Postfix 2.5.3 and later.

strict_mime_encoding_domain (default: no)
       Reject mail with invalid Content-Transfer-Encoding: information for the
       message/* or multipart/* MIME content types.   This  blocks  mail  from
       poorly written software.

       This  feature  should  not be enabled on a general purpose mail server,
       because it will reject mail after a single violation.

       This feature is available in Postfix 2.0 and later.

strict_rfc821_envelopes (default: no)
       Require that addresses received in SMTP MAIL FROM and RCPT TO  commands
       are  enclosed  with <>, and that those addresses do not contain RFC 822
       style comments or phrases.  This stops mail from poorly  written  soft-
       ware.

       By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL FROM
       and RCPT TO addresses.

sun_mailtool_compatibility (default: no)
       Obsolete  SUN  mailtool  compatibility  feature.  Instead,  use  "mail-
       box_delivery_lock = dotlock".

swap_bangpath (default: yes)
       Enable  the  rewriting of "site!user" into "user@site".  This is neces-
       sary if your machine is connected to UUCP networks.  It is  enabled  by
       default.

       Note:  with  Postfix version 2.2, message header address rewriting hap-
       pens 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:

       swap_bangpath = no

syslog_facility (default: mail)
       The syslog facility of Postfix logging. Specify a facility  as  defined
       in syslog.conf(5). The default facility is "mail".

       Warning:  a non-default syslog_facility setting takes effect only after
       a Postfix process has completed initialization.  Errors during  process
       initialization  will be logged with the default facility.  Examples are
       errors while parsing the  command  line  arguments,  and  errors  while
       accessing the Postfix main.cf configuration file.

syslog_name (default: postfix)
       The  mail  system  name that is prepended to the process name in syslog
       records, so that "smtpd" becomes, for example, "postfix/smtpd".

       Warning: a non-default syslog_name setting takes effect  only  after  a
       Postfix  process  has  completed  initialization. Errors during process
       initialization will be logged  with  the  default  name.  Examples  are
       errors  while  parsing  the  command  line  arguments, and errors while
       accessing the Postfix main.cf configuration file.

tls_daemon_random_bytes (default: 32)
       The number of pseudo-random bytes that an smtp(8) or  smtpd(8)  process
       requests from the tlsmgr(8) server in order to seed its internal pseudo
       random number generator (PRNG).  The default of 32 bytes (equivalent to
       256 bits) is sufficient to generate a 128bit (or 168bit) session key.

       This feature is available in Postfix 2.2 and later.

tls_export_cipherlist (default: ALL:+RC4:@STRENGTH)
       The  OpenSSL  cipherlist  for  "EXPORT"  or  higher grade ciphers. This
       defines  the  meaning  of  the  "export"  setting  in  smtpd_tls_manda-
       tory_ciphers,     smtp_tls_mandatory_ciphers     and    lmtp_tls_manda-
       tory_ciphers. This is the cipherlist for the opportunistic ("may")  TLS
       client  security  level  and  is  the  default  cipherlist for the SMTP
       server. You are strongly encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
       The OpenSSL cipherlist for "HIGH" grade ciphers. This defines the mean-
       ing    of    the   "high"   setting   in   smtpd_tls_mandatory_ciphers,
       smtp_tls_mandatory_ciphers  and  lmtp_tls_mandatory_ciphers.  You   are
       strongly encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_low_cipherlist (default: ALL:!EXPORT:+RC4:@STRENGTH)
       The  OpenSSL cipherlist for "LOW" or higher grade ciphers. This defines
       the  meaning  of  the  "low"  setting  in  smtpd_tls_mandatory_ciphers,
       smtp_tls_mandatory_ciphers   and  lmtp_tls_mandatory_ciphers.  You  are
       strongly encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
       The OpenSSL cipherlist for  "MEDIUM"  or  higher  grade  ciphers.  This
       defines  the  meaning  of  the  "medium"  setting  in  smtpd_tls_manda-
       tory_ciphers,    smtp_tls_mandatory_ciphers     and     lmtp_tls_manda-
       tory_ciphers.  This is the default cipherlist for mandatory TLS encryp-
       tion in the TLS client (with anonymous ciphers disabled when  verifying
       server  certificates).  You  are strongly encouraged to not change this
       setting.

       This feature is available in Postfix 2.3 and later.

tls_null_cipherlist (default: eNULL:!aNULL)
       The OpenSSL cipherlist for "NULL" grade ciphers that provide  authenti-
       cation  without encryption. This defines the meaning of the "null" set-
       ting  in  smtpd_mandatory_tls_ciphers,  smtp_tls_mandatory_ciphers  and
       lmtp_tls_mandatory_ciphers.   You are strongly encouraged to not change
       this setting.

       This feature is available in Postfix 2.3 and later.

tls_random_bytes (default: 32)
       The number of bytes that tlsmgr(8) reads from  $tls_random_source  when
       (re)seeding  the  in-memory pseudo random number generator (PRNG) pool.
       The default of 32 bytes (256 bits) is good enough for 128bit  symmetric
       keys.  If using EGD or a device file, a maximum of 255 bytes is read.

       This feature is available in Postfix 2.2 and later.

tls_random_exchange_name (default: see postconf -d output)
       Name  of  the  pseudo random number generator (PRNG) state file that is
       maintained by tlsmgr(8). The file is created when it  does  not  exist,
       and its length is fixed at 1024 bytes.

       As  of version 2.5, Postfix no longer uses root privileges when opening
       this file, and the  default  file  location  was  changed  from  ${con-
       fig_directory}/prng_exch  to  ${data_directory}/prng_exch.  As a migra-
       tion 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.

       This feature is available in Postfix 2.2 and later.

tls_random_prng_update_period (default: 3600s)
       The time between attempts by tlsmgr(8) to save the state of the  pseudo
       random  number  generator  (PRNG)  to the file specified with $tls_ran-
       dom_exchange_name.

       This feature is available in Postfix 2.2 and later.

tls_random_reseed_period (default: 3600s)
       The maximal time between attempts by tlsmgr(8) to re-seed the in-memory
       pseudo  random number generator (PRNG) pool from external sources.  The
       actual time between re-seeding attempts is calculated using  the  PRNG,
       and is between 0 and the time specified.

       This feature is available in Postfix 2.2 and later.

tls_random_source (default: see postconf -d output)
       The  external  entropy source for the in-memory tlsmgr(8) pseudo random
       number generator (PRNG) pool. Be sure to specify a non-blocking source.
       If  this  source is not a regular file, the entropy source type must be
       prepended:  egd:/path/to/egd_socket for a source  with  EGD  compatible
       socket interface, or dev:/path/to/device for a device file.

       Note:  on  OpenBSD systems specify /dev/arandom when /dev/urandom gives
       timeout errors.

       This feature is available in Postfix 2.2 and later.

trace_service_name (default: trace)
       The name of the trace service.  This  service  is  implemented  by  the
       bounce(8) daemon and maintains a record of mail deliveries and produces
       a mail delivery report when verbose delivery is requested  with  "send-
       mail -v".

       This feature is available in Postfix 2.1 and later.

transport_delivery_slot_cost (default: $default_delivery_slot_cost)
       A transport-specific override for the default_delivery_slot_cost param-
       eter value, where transport is the master.cf name of the message deliv-
       ery transport.

transport_delivery_slot_discount (default: $default_delivery_slot_discount)
       A  transport-specific  override  for the default_delivery_slot_discount
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

transport_delivery_slot_loan (default: $default_delivery_slot_loan)
       A transport-specific override for the default_delivery_slot_loan param-
       eter value, where transport is the master.cf name of the message deliv-
       ery transport.

transport_destination_concurrency_failed_cohort_limit  (default: $default_des-
       tination_concurrency_failed_cohort_limit)
       A  transport-specific  override  for  the   default_destination_concur-
       rency_failed_cohort_limit  parameter value, where transport is the mas-
       ter.cf name of the message delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_limit (default: $default_destination_concur-
       rency_limit)
       A   transport-specific  override  for  the  default_destination_concur-
       rency_limit parameter value, where transport is the master.cf  name  of
       the message delivery transport.

transport_destination_concurrency_negative_feedback  (default: $default_desti-
       nation_concurrency_negative_feedback)
       A  transport-specific  override  for  the   default_destination_concur-
       rency_negative_feedback  parameter  value,  where transport is the mas-
       ter.cf name of the message delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_positive_feedback (default:  $default_desti-
       nation_concurrency_positive_feedback)
       A   transport-specific  override  for  the  default_destination_concur-
       rency_positive_feedback parameter value, where transport  is  the  mas-
       ter.cf name of the message delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_destination_rate_delay (default: $default_destination_rate_delay)
       A  transport-specific  override  for the default_destination_rate_delay
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_destination_recipient_limit  (default:  $default_destination_recipi-
       ent_limit)
       A  transport-specific  override  for  the   default_destination_recipi-
       ent_limit parameter value, where transport is the master.cf name of the
       message delivery transport.

transport_extra_recipient_limit (default: $default_extra_recipient_limit)
       A transport-specific  override  for  the  default_extra_recipient_limit
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

transport_initial_destination_concurrency (default:  $initial_destination_con-
       currency)
       A  transport-specific  override for the initial_destination_concurrency
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       This feature is available in Postfix 2.5 and later.

transport_maps (default: empty)
       Optional lookup tables with mappings from recipient address to (message
       delivery  transport,  next-hop  destination).   See  transport(5)   for
       details.

       Specify  zero or more "type:table" lookup tables.  If you use this fea-
       ture with local files, run "postmap /etc/postfix/transport" after  mak-
       ing a change.

       For safety reasons, as of Postfix 2.3 this feature does not allow $num-
       ber substitutions in regular expression maps.

       Examples:

       transport_maps = dbm:/etc/postfix/transport
       transport_maps = hash:/etc/postfix/transport

transport_minimum_delivery_slots (default: $default_minimum_delivery_slots)
       A transport-specific override  for  the  default_minimum_delivery_slots
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

transport_recipient_limit (default: $default_recipient_limit)
       A transport-specific override for the default_recipient_limit parameter
       value,  where  transport  is the master.cf name of the message delivery
       transport.

transport_recipient_refill_delay (default: $default_recipient_refill_delay)
       A transport-specific override  for  the  default_recipient_refill_delay
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       This feature is available in Postfix 2.4 and later.

transport_recipient_refill_limit (default: $default_recipient_refill_limit)
       A transport-specific override  for  the  default_recipient_refill_limit
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       This feature is available in Postfix 2.4 and later.

transport_retry_time (default: 60s)
       The time between attempts by the Postfix queue  manager  to  contact  a
       malfunctioning message delivery transport.

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

transport_time_limit (default: $command_time_limit)
       A transport-specific  override  for  the  command_time_limit  parameter
       value,  where  transport  is the master.cf name of the message delivery
       transport.

trigger_timeout (default: 10s)
       The time limit for sending a trigger to a Postfix daemon (for  example,
       the  pickup(8)  or  qmgr(8)  daemon). This time limit prevents programs
       from getting stuck when the mail system is under heavy load.

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

undisclosed_recipients_header (default: To: undisclosed-recipients:;)
       Message  header  that the Postfix cleanup(8) server inserts when a mes-
       sage contains no To: or Cc: message header.

unknown_address_reject_code (default: 450)
       The numerical Postfix SMTP server response code when a sender or recip-
       ient   address  is  rejected  by  the  reject_unknown_sender_domain  or
       reject_unknown_recipient_domain restriction.  The  response  is  always
       450 in case of a temporary DNS error.

       Do not change this unless you have a complete understanding of RFC 821.

unknown_client_reject_code (default: 450)
       The  numerical  Postfix SMTP server response code when a client without
       valid   address   <=>    name    mapping    is    rejected    by    the
       reject_unknown_client_hostname  restriction.  The  SMTP  server  always
       replies with 450 when the mapping failed due to a temporary error  con-
       dition.

       Do not change this unless you have a complete understanding of RFC 821.

unknown_hostname_reject_code (default: 450)
       The numerical Postfix SMTP server response code when the hostname spec-
       ified  with  the  HELO   or   EHLO   command   is   rejected   by   the
       reject_unknown_helo_hostname restriction.

       Do not change this unless you have a complete understanding of RFC 821.

unknown_local_recipient_reject_code (default: 550)
       The  numerical  Postfix  SMTP  server  response  code  when a recipient
       address is local, and $local_recipient_maps specifies a list of  lookup
       tables that does not match the recipient.  A recipient address is local
       when  its   domain   matches   $mydestination,   $proxy_interfaces   or
       $inet_interfaces.

       The  default  setting is 550 (reject mail) but it is safer to initially
       use 450 (try again later)  so  you  have  time  to  find  out  if  your
       local_recipient_maps settings are OK.

       Example:

       unknown_local_recipient_reject_code = 450

       This feature is available in Postfix 2.0 and later.

unknown_relay_recipient_reject_code (default: 550)
       The  numerical  Postfix SMTP server reply code when a recipient address
       matches $relay_domains, and relay_recipient_maps specifies  a  list  of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_alias_reject_code (default: 550)
       The  SMTP  server  reply  code  when  a recipient address matches $vir-
       tual_alias_domains, and $virtual_alias_maps specifies a list of  lookup
       tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_mailbox_reject_code (default: 550)
       The  SMTP  server  reply  code  when  a recipient address matches $vir-
       tual_mailbox_domains, and $virtual_mailbox_maps  specifies  a  list  of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unverified_recipient_reject_code (default: 450)
       The  numerical Postfix SMTP server response when a recipient address is
       rejected by the reject_unverified_recipient restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do not change this unless you have a complete understanding of RFC 821.

       This feature is available in Postfix 2.1 and later.

unverified_sender_reject_code (default: 450)
       The  numerical  Postfix SMTP server response code when a sender address
       is rejected by the reject_unverified_sender restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do not change this unless you have a complete understanding of RFC 821.

       This feature is available in Postfix 2.1 and later.

verp_delimiter_filter (default: -=+)
       The  characters  Postfix  accepts  as  VERP delimiter characters on the
       Postfix sendmail(1) command line and in SMTP commands.

       This feature is available in Postfix 1.1 and later.

virtual_alias_domains (default: $virtual_alias_maps)
       Postfix is final destination for the specified list  of  virtual  alias
       domains,  that  is,  domains  for  which  all  addresses are aliased to
       addresses in other local or remote domains. The SMTP  server  validates
       recipient  addresses  with $virtual_alias_maps and rejects non-existent
       recipients.  See  also  the  virtual  alias   domain   class   in   the
       ADDRESS_CLASS_README file

       This  feature  is available in Postfix 2.0 and later. The default value
       is backwards compatible with Postfix version 1.1.

       The default value is $virtual_alias_maps  so  that  you  can  keep  all
       information about virtual alias domains in one place.  If you have many
       users, it is better to separate  information  that  changes  more  fre-
       quently  (virtual  address  ->  local  or  remote address mapping) from
       information that changes less frequently (the list  of  virtual  domain
       names).

       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 table entry matches  a  lookup  string  (the  lookup  result  is
       ignored).   Continue  long  lines by starting the next line with white-
       space. Specify "!pattern" to exclude a host or  domain  name  from  the
       list.  The  form "!/file/name" is supported only in Postfix version 2.4
       and later.

       See also the VIRTUAL_README and ADDRESS_CLASS_README documents for fur-
       ther information.

       Example:

       virtual_alias_domains = virtual1.tld virtual2.tld

virtual_alias_expansion_limit (default: 1000)
       The  maximal  number of addresses that virtual alias expansion produces
       from each original recipient.

       This feature is available in Postfix 2.1 and later.

virtual_alias_maps (default: $virtual_maps)
       Optional lookup tables that alias specific mail addresses or domains to
       other  local or remote address.  The table format and lookups are docu-
       mented in virtual(5). For an overview of Postfix address  manipulations
       see the ADDRESS_REWRITING_README document.

       This  feature  is available in Postfix 2.0 and later. The default value
       is backwards compatible with Postfix version 1.1.

       If you use this feature with indexed  files,  run  "postmap  /etc/post-
       fix/virtual" after changing the file.

       Examples:

       virtual_alias_maps = dbm:/etc/postfix/virtual
       virtual_alias_maps = hash:/etc/postfix/virtual

virtual_alias_recursion_limit (default: 1000)
       The  maximal  nesting  depth of virtual alias expansion.  Currently the
       recursion limit is applied only to the left  branch  of  the  expansion
       graph,  so the depth of the tree can in the worst case reach the sum of
       the expansion and recursion limits.  This may change in the future.

       This feature is available in Postfix 2.1 and later.

virtual_destination_concurrency_limit  (default:  $default_destination_concur-
       rency_limit)
       The  maximal  number of parallel deliveries to the same destination via
       the virtual 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.

virtual_destination_recipient_limit   (default:   $default_destination_recipi-
       ent_limit)
       The  maximal  number of recipients per delivery via the virtual 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  vir-
       tual_destination_concurrency_limit  from  concurrency  per  domain into
       concurrency per recipient.

virtual_gid_maps (default: empty)
       Lookup tables with the per-recipient group ID  for  virtual(8)  mailbox
       delivery.

       In  a  lookup table, specify a left-hand side of "@domain.tld" to match
       any user in  the  specified  domain  that  does  not  have  a  specific
       "userATdomain.tld" entry.

       When   a   recipient   address   has   an  optional  address  extension
       (user+fooATdomain.tld), the virtual(8) delivery agent looks up the  full
       address  first,  and  when the lookup fails, it looks up the unextended
       address (userATdomain.tld).

       Note 1: for security reasons, the virtual(8) delivery  agent  disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note 2: for  security  reasons,  the  virtual(8)  delivery  agent  will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open the table directly. Before Postfix  version  2.2,  the  virtual(8)
       delivery agent will terminate with a fatal error.

virtual_mailbox_base (default: empty)
       A  prefix  that  the virtual(8) delivery agent prepends to all pathname
       results from $virtual_mailbox_maps table lookups.   This  is  a  safety
       measure  to  ensure  that an out of control map doesn't litter the file
       system with mailboxes.  While virtual_mailbox_base could be set to "/",
       this setting isn't recommended.

       Example:

       virtual_mailbox_base = /var/mail

virtual_mailbox_domains (default: $virtual_mailbox_maps)
       Postfix is final destination for the specified list of domains; mail is
       delivered via  the  $virtual_transport  mail  delivery  transport.   By
       default this is the Postfix virtual(8) delivery agent.  The SMTP server
       validates recipient addresses with  $virtual_mailbox_maps  and  rejects
       mail  for non-existent recipients.  See also the virtual mailbox domain
       class in the ADDRESS_CLASS_README file.

       This parameter expects the same syntax as the mydestination  configura-
       tion parameter.

       This  feature  is available in Postfix 2.0 and later. The default value
       is backwards compatible with Postfix version 1.1.

virtual_mailbox_limit (default: 51200000)
       The maximal size in bytes of an individual mailbox or maildir file,  or
       zero (no limit).

virtual_mailbox_lock (default: see postconf -d output)
       How to lock a UNIX-style virtual(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 application-level locks.

       Note 1: the dotlock method requires that the recipient UID or  GID  has
       write access to the parent directory of the recipient's mailbox file.

       Note 2: the default setting of this parameter is system dependent.

virtual_mailbox_maps (default: empty)
       Optional  lookup  tables  with  all valid addresses in the domains that
       match $virtual_mailbox_domains.

       In a lookup table, specify a left-hand side of "@domain.tld"  to  match
       any  user  in  the  specified  domain  that  does  not  have a specific
       "userATdomain.tld" entry.

       The virtual(8) delivery agent uses this table to look up the per-recip-
       ient mailbox or maildir pathname.  If the lookup result ends in a slash
       ("/"), maildir-style delivery is carried out,  otherwise  the  path  is
       assumed to specify a UNIX-style mailbox file.  Note that $virtual_mail-
       box_base is unconditionally prepended to this path.

       When  a  recipient  address   has   an   optional   address   extension
       (user+fooATdomain.tld),  the virtual(8) delivery agent looks up the full
       address first, and when the lookup fails, it looks  up  the  unextended
       address (userATdomain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note  2:  for  security  reasons,  the  virtual(8)  delivery agent will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open  the  table  directly.  Before Postfix version 2.2, the virtual(8)
       delivery agent will terminate with a fatal error.

virtual_maps (default: empty)
       Optional lookup tables with a) names of domains for which all addresses
       are  aliased  to  addresses  in  other  local or remote domains, and b)
       addresses that are aliased  to  addresses  in  other  local  or  remote
       domains.   Available  before  Postfix version 2.0. With Postfix version
       2.0  and  later,  this  is  replaced   by   separate   controls:   vir-
       tual_alias_domains and virtual_alias_maps.

virtual_minimum_uid (default: 100)
       The minimum user ID value that the virtual(8) delivery agent accepts as
       a result from $virtual_uid_maps table  lookup.   Returned  values  less
       than this will be rejected, and the message will be deferred.

virtual_transport (default: virtual)
       The  default mail delivery transport and next-hop destination for final
       delivery to domains listed with $virtual_mailbox_domains.  This  infor-
       mation 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
       part is optional.  For more details see the transport(5) manual page.

       This feature is available in Postfix 2.0 and later.

virtual_uid_maps (default: empty)
       Lookup tables with the per-recipient user ID that the virtual(8) deliv-
       ery agent uses while writing to the recipient's mailbox.

       In a lookup table, specify a left-hand side of "@domain.tld"  to  match
       any  user  in  the  specified  domain  that  does  not  have a specific
       "userATdomain.tld" entry.

       When  a  recipient  address   has   an   optional   address   extension
       (user+fooATdomain.tld),  the virtual(8) delivery agent looks up the full
       address first, and when the lookup fails, it looks  up  the  unextended
       address (userATdomain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note  2:  for  security  reasons,  the  virtual(8)  delivery agent will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open  the  table  directly.  Before Postfix version 2.2, the virtual(8)
       delivery agent will terminate with a fatal error.

SEE ALSO
       postconf(1), Postfix configuration parameter maintenance
       master(5), Postfix daemon configuration maintenance

LICENSE
       The Secure Mailer license must be distributed with this software.

AUTHOR(S)
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA



                                                                   POSTCONF(5)