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GENERIC(5) File Formats Manual GENERIC(5)

NAME
generic - Postfix generic table format

SYNOPSIS
postmap /etc/postfix/generic

postmap -q "string" /etc/postfix/generic

postmap -q - /etc/postfix/generic <inputfile

DESCRIPTION
The optional generic(5) table specifies an address mapping that applies when mail is deliv‐
ered. 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 in‐
side 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 TA‐
BLES" or "TCP-BASED TABLES".

CASE FOLDING
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.

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

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

blank lines and comments
Empty lines and whitespace-only lines are ignored, as are lines whose first non-white‐
space character is a `#'.

multi-line text
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, 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 pat‐
tern, until a match is found.

user@domain address
Replace user@domain by address. This form has the highest precedence.

user address
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.

RESULT ADDRESS REWRITING
The lookup result is subject to address rewriting:

• When the result has the form @otherdomain, the result becomes the same user in other‐
domain.

• When "append_at_myorigin=yes", append "@$myorigin" to addresses without "@domain".

• When "append_dot_mydomain=yes", append ".$mydomain" to addresses without ".domain".

ADDRESS EXTENSION
When a mail address localpart contains the optional recipient delimiter (e.g., user+foo@do‐
main), 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.

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 reg‐‐
exp_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 parenthe‐
sized substrings from the pattern can be interpolated as $1, $2 and so on.

TCP-BASED TABLES
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 constituent parts, nor is user+foo broken up into user
and foo.

Results are the same as with indexed file lookups.

EXAMPLE
The following shows a generic mapping with an indexed file. When mail is sent to a remote
host via SMTP, this replaces his AT localdomain.local by his ISP mail address, replaces her@lo‐
caldomain.local by her ISP mail address, and replaces other local addresses by his ISP ac‐
count, with an address extension of +local (this example assumes that the ISP supports "+"
style address extensions).

/etc/postfix/main.cf:
smtp_generic_maps = hash:/etc/postfix/generic

/etc/postfix/generic:
his AT localdomain.local hisaccount AT hisisp.example
her AT localdomain.local heraccount AT herisp.example
@localdomain.local hisaccount+local AT 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".

BUGS
The table format does not understand quoting conventions.

CONFIGURATION PARAMETERS
The following main.cf parameters are especially relevant. The text below provides only a pa‐
rameter summary. See postconf(5) for more details including examples.

smtp_generic_maps
Address mapping lookup table for envelope and header sender and recipient addresses
while delivering mail via SMTP.

propagate_unmatched_extensions
A list of address rewriting or forwarding mechanisms that propagate an address exten‐
sion from the original address to the result. Specify zero or more of canonical, vir‐‐
tual, alias, forward, include, or generic.

Other parameters of interest:

inet_interfaces
The network interface addresses that this system receives mail on. You need to stop
and start Postfix when this parameter changes.

proxy_interfaces
Other interfaces that this machine receives mail on by way of a proxy agent or network
address translator.

mydestination
List of domains that this mail system considers local.

myorigin
The domain that is appended to locally-posted mail.

owner_request_special
Give special treatment to owner-xxx and xxx-request addresses.

SEE ALSO
postmap(1), Postfix lookup table manager
postconf(5), configuration parameters
smtp(8), Postfix SMTP client

README FILES
Use "postconf readme_directory" or "postconf html_directory" to locate this information.
ADDRESS_REWRITING_README, address rewriting guide
DATABASE_README, Postfix lookup table overview
STANDARD_CONFIGURATION_README, configuration examples

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

HISTORY
A genericstable feature appears in the Sendmail MTA.

This feature is available in Postfix 2.2 and later.

AUTHOR(S)
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

GENERIC(5)