Scroll to navigation

GENERIC(5) File Formats Manual GENERIC(5)


generic - Postfix generic table format


postmap /etc/postfix/generic
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 localdomain.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 EXAMPLE 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 a TCP-based server. In those cases, 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 lower case.


The input format for the postmap(1) command is as follows:

When pattern matches a mail address, replace it by the corresponding result.
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.


With lookups from indexed files such as DB or DBM, or from networked tables such as NIS, LDAP or SQL, each user@domain query produces a sequence of query patterns as described below.

Each query pattern is sent to each specified lookup table before trying the next query pattern, until a match is found.

Replace user@domain by address. This form has the highest precedence.
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.
@domain address
Replace other addresses in domain by address. This form has the lowest precedence.


The lookup result is subject to address rewriting:

  • When the result has the form @otherdomain, the result becomes the same user in otherdomain.
  • When "append_at_myorigin=yes", append "@$myorigin" to addresses without "@domain".
  • When "append_dot_mydomain=yes", append ".$mydomain" to addresses without ".domain".


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 lookup.


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 broken 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 interpolated 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 available in Postfix 2.5 and later.

Each lookup operation uses the entire address once. Thus, user@domain mail addresses are not broken up into their user and @domain constituent 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 his@localdomain.local by his ISP mail address, replaces her@localdomain.local 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 /etc/postfix/generic:
his@localdomain.local hisaccount@hisisp.example
her@localdomain.local heraccount@herisp.example
@localdomain.local hisaccount+local@hisisp.example
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 -m".


The table format does not understand quoting conventions.


The following parameters are especially relevant. The text below provides only a parameter summary. See postconf(5) for more details including examples.

Optional lookup tables that perform address rewriting in the Postfix SMTP client, typically to transform a locally valid address into a globally valid address when sending mail across the Internet.
What address lookup tables copy an address extension from the lookup key to the lookup result.

Other parameters of interest:

The network interface addresses that this mail system receives mail on.
The network interface addresses that this mail system receives mail on by way of a proxy or network address translation unit.
The list of domains that are delivered via the $local_transport mail delivery transport.
The domain name that locally-posted mail appears to come from, and that locally posted mail is delivered to.
Enable special treatment for owner-listname entries in the aliases(5) file, and don't split owner-listname and listname-request address localparts when the recipient_delimiter is set to "-".


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 this information.

ADDRESS_REWRITING_README, address rewriting guide
DATABASE_README, Postfix lookup table overview


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.


Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA