CANONICAL(5) File Formats Manual CANONICAL(5)
canonical - format of Postfix canonical table
postmap -q "string" /etc/postfix/canonical
postmap -q - /etc/postfix/canonical <<inputfile
The optional canonical table specifies an address mapping for local and
non-local addresses. The mapping is used by the cleanup(8) daemon. The
address mapping is recursive.
Normally, the canonical 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/canonical in order to rebuild the
indexed file after changing the 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. In that case, the
lookups are done in a slightly different way as described below.
The canonical 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).
Think Sendmail rule set S3, if you like.
Typically, one would use the canonical table to replace login names by
Firstname.Lastname, or to clean up addresses produced by legacy mail
The canonical mapping is not to be confused with virtual domain sup-
port. Use the virtual(5) map for that purpose.
The canonical mapping is not to be confused with local aliasing. Use
the aliases(5) map for that purpose.
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.
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
user@domain is replaced by address. This form has the highest
This is useful to clean up addresses produced by legacy mail
systems. It can also be used to produce Firstname.Lastname
style addresses, but see below for a simpler solution.
user@site is replaced by address when site is equal to $myori-
gin, when site is listed in $mydestination, or when it is listed
This form is useful for replacing login names by Firstname.Last-
Every address in domain is replaced by address. This form has
the lowest precedence.
In all the above forms, when address has the form @otherdomain, the
result is the same user in otherdomain.
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. An unmatched address exten-
sion (+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 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.
The table format does not understand quoting conventions.
The following main.cf parameters are especially relevant to this topic.
See the Postfix main.cf file for syntax details and for default values.
Use the postfix reload command after a configuration change.
List of canonical mapping tables.
Address mapping lookup table for envelope and header recipient
Address mapping lookup table for envelope and header sender
By default (recipient address) canonicalization is applied even
to the envelope recipient. To prevent delivery loops when using
external canonical addresses, while still having recipient head-
ers rewritten to the canonical addresses, set this to 'no'.
Other parameters of interest:
The network interface addresses that this system receives mail
on. You need to stop and start Postfix when this parameter
List of address classes subject to masquerading: zero or more of
envelope_sender, envelope_recipient, header_sender,
List of domains that hide their subdomain structure.
List of user names that are not subject to address masquerading.
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.
cleanup(8) canonicalize and enqueue mail
postmap(1) create mapping table
virtual(5) virtual domain mapping
pcre_table(5) format of PCRE tables
regexp_table(5) format of POSIX regular expression tables
The Secure Mailer license must be distributed with this software.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA