CANONICAL(5)CANONICAL(5)NAMEcanonical - Postfix canonical table format
postmap -q "string" /usr/local/etc/postfix/canonical
postmap -q - /usr/local/etc/postfix/canonical <inputfile
The optional canonical(5) table specifies an address mapping for local
and non-local addresses. The mapping is used by the cleanup(8) daemon,
before mail is stored into the queue. The address mapping is recur‐
Normally, the canonical(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 /usr/local/etc/postfix/canonical" 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 cases, the lookups are done in a
slightly different way as described below under "REGULAR EXPRESSION
TABLES" or "TCP-BASED TABLES".
By default the canonical(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). This is controlled with the canonical_classes
NOTE: Postfix versions 2.2 and later rewrite message headers from
remote SMTP clients only if the client matches the local_header_re‐
write_clients parameter, or if the remote_header_rewrite_domain config‐
uration parameter specifies a non-empty value. To get the behavior
before Postfix 2.2, specify "local_header_rewrite_clients =
Typically, one would use the canonical(5) table to replace login names
by Firstname.Lastname, or to clean up addresses produced by legacy mail
The canonical(5) mapping is not to be confused with virtual alias sup‐
port or with local aliasing. To change the destination but not the
headers, use the virtual(5) or aliases(5) map instead.
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‐
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.
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 $proxy_interfaces.
This form is useful for replacing login names by Firstname.Last‐
Replace other addresses in domain by address. This form has the
Note: @domain is a wild-card. When this form is applied to
recipient addresses, the Postfix SMTP server accepts mail for
any recipient in domain, regardless of whether that recipient
exists. This may turn your mail system into a backscatter
source: Postfix first accepts mail for non-existent recipients
and then tries to return that mail as "undeliverable" to the
often forged sender address.
RESULT ADDRESS REWRITING
The lookup result is subject to address rewriting:
· When the result has the form @otherdomain, the result becomes
the same user in otherdomain.
· When "append_at_myorigin=yes", append "@$myorigin" to addresses
· 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 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.
What addresses are subject to canonical address mapping.
List of canonical mapping tables.
Address mapping lookup table for envelope and header recipient
Address mapping lookup table for envelope and header sender
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
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 rewrite message headers and update incomplete
addresses with the domain specified in the remote_header_re‐
Other interfaces that this machine receives mail on by way of a
proxy agent or network address translator.
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.
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.
SEE ALSOcleanup(8), canonicalize and enqueue mail
postmap(1), Postfix lookup table manager
postconf(5), configuration parameters
virtual(5), virtual aliasing
Use "postconf readme_directory" or "postconf html_directory" to locate
DATABASE_README, Postfix lookup table overview
ADDRESS_REWRITING_README, address rewriting guide
The Secure Mailer license must be distributed with this software.
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA