GENERIC(5) File Formats Manual GENERIC(5)
generic - Postfix generic table format
postmap -q "string" /etc/postfix/generic
postmap -q - /etc/postfix/generic <<inputfile
The optional generic(5) table specifies an address mapping that applies
when mail is delivered. This is the opposite of canonical(5) mapping,
which applies when mail is received.
Typically, one would use the generic(5) table on a system that does not
have a valid Internet domain name and that uses something like localdo-
main.local instead. The generic(5) table is then used by the smtp(8)
client to transform local mail addresses into valid Internet mail
addresses when mail has to be sent across the Internet. See the EXAM-
PLE section at the end of this document.
The generic(5) mapping affects both message header addresses (i.e.
addresses that appear inside messages) and message envelope addresses
(for example, the addresses that are used in SMTP protocol commands).
Normally, the generic(5) table is specified as a text file that serves
as input to the postmap(1) command. The result, an indexed file in dbm
or db format, is used for fast searching by the mail system. Execute
the command "postmap /etc/postfix/generic" to rebuild an indexed file
after changing the corresponding text file.
When the table is provided via other means such as NIS, LDAP or SQL,
the same lookups are done as for ordinary indexed files.
Alternatively, the table can be provided as a regular-expression map
where patterns are given as regular expressions, or lookups can be
directed to TCP-based server. In those case, the lookups are done in a
slightly different way as described below under "REGULAR EXPRESSION
TABLES" or "TCP-BASED TABLES".
The search string is folded to lowercase before database lookup. As of
Postfix 2.3, the search string is not case folded with database types
such as regexp: or pcre: whose lookup fields can match both upper and
The input format for the postmap(1) command is as follows:
When pattern matches a mail address, replace it by the corre-
blank lines and comments
Empty lines and whitespace-only lines are ignored, as are lines
whose first non-whitespace character is a `#'.
A logical line starts with non-whitespace text. A line that
starts with whitespace continues a logical line.
TABLE SEARCH ORDER
With lookups from indexed files such as DB or DBM, or from networked
tables such as NIS, LDAP or SQL, patterns are tried in the order as
Replace user@domain by address. This form has the highest prece-
Replace user@site by address when site is equal to $myorigin,
when site is listed in $mydestination, or when it is listed in
$inet_interfaces or $proxy_interfaces.
Replace other addresses in domain by address. This form has the
RESULT ADDRESS REWRITING
The lookup result is subject to address rewriting:
o When the result has the form @otherdomain, the result becomes
the same user in otherdomain.
o When "append_at_myorigin=yes", append "@$myorigin" to addresses
o When "append_dot_mydomain=yes", append ".$mydomain" to addresses
When a mail address localpart contains the optional recipient delimiter
(e.g., user+foo@domain), the lookup order becomes: user+foo@domain,
user@domain, user+foo, user, and @domain.
The propagate_unmatched_extensions parameter controls whether an
unmatched address extension (+foo) is propagated to the result of table
REGULAR EXPRESSION TABLES
This section describes how the table lookups change when the table is
given in the form of regular expressions. For a description of regular
expression lookup table syntax, see regexp_table(5) or pcre_table(5).
Each pattern is a regular expression that is applied to the entire
address being looked up. Thus, user@domain mail addresses are not bro-
ken up into their user and @domain constituent parts, nor is user+foo
broken up into user and foo.
Patterns are applied in the order as specified in the table, until a
pattern is found that matches the search string.
Results are the same as with indexed file lookups, with the additional
feature that parenthesized substrings from the pattern can be interpo-
lated as $1, $2 and so on.
This section describes how the table lookups change when lookups are
directed to a TCP-based server. For a description of the TCP
client/server lookup protocol, see tcp_table(5). This feature is not
available up to and including Postfix version 2.4.
Each lookup operation uses the entire address once. Thus, user@domain
mail addresses are not broken up into their user and @domain con-
stituent parts, nor is user+foo broken up into user and foo.
Results are the same as with indexed file lookups.
The following shows a generic mapping with an indexed file. When mail
is sent to a remote host via SMTP, this replaces email@example.com
by his ISP mail address, replaces firstname.lastname@example.org by her ISP mail
address, and replaces other local addresses by his ISP account, with an
address extension of +local (this example assumes that the ISP supports
"+" style address extensions).
smtp_generic_maps = hash:/etc/postfix/generic
Execute the command "postmap /etc/postfix/generic" whenever the table
is changed. Instead of hash, some systems use dbm database files. To
find out what tables your system supports use the command "postconf
The table format does not understand quoting conventions.
The following main.cf parameters are especially relevant. The text
below provides only a parameter summary. See postconf(5) for more
details including examples.
Address mapping lookup table for envelope and header sender and
recipient addresses while delivering mail via SMTP.
A list of address rewriting or forwarding mechanisms that propa-
gate an address extension from the original address to the
result. Specify zero or more of canonical, virtual, alias, for-
ward, include, or generic.
Other parameters of interest:
The network interface addresses that this system receives mail
on. You need to stop and start Postfix when this parameter
Other interfaces that this machine receives mail on by way of a
proxy agent or network address translator.
List of domains that this mail system considers local.
The domain that is appended to locally-posted mail.
Give special treatment to owner-xxx and xxx-request addresses.
postmap(1), Postfix lookup table manager
postconf(5), configuration parameters
smtp(8), Postfix SMTP client
Use "postconf readme_directory" or "postconf html_directory" to locate
ADDRESS_REWRITING_README, address rewriting guide
DATABASE_README, Postfix lookup table overview
STANDARD_CONFIGURATION_README, configuration examples
The Secure Mailer license must be distributed with this software.
A genericstable feature appears in the Sendmail MTA.
This feature is available in Postfix 2.2 and later.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA