Updated: 2021/Apr/14


CANONICAL(5)                  File Formats Manual                 CANONICAL(5)




NAME
       canonical - Postfix canonical table format

SYNOPSIS
       postmap /etc/postfix/canonical

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

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

DESCRIPTION
       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
       recursive.

       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 /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
       parameter.

       NOTE: Postfix versions 2.2 and later rewrite message headers from
       remote SMTP clients only if the client matches the
       local_header_rewrite_clients parameter, or if the
       remote_header_rewrite_domain configuration parameter specifies a
       non-empty value. To get the behavior before Postfix 2.2, specify
       "local_header_rewrite_clients = static:all".

       Typically, one would use the canonical(5) table to replace login names
       by Firstname.Lastname, or to clean up addresses produced by legacy mail
       systems.

       The canonical(5) mapping is not to be confused with virtual alias
       support or with local aliasing. To change the destination but not the
       headers, use the virtual(5) or aliases(5) map instead.

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

       blank lines and comments
              Empty lines and whitespace-only lines are ignored, as are lines
              whose first non-whitespace 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 pattern, until a match is found.

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

              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 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.

              This form is useful for replacing login names by
              Firstname.Lastname.

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

              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.

              To avoid backscatter with mail for a wild-card domain, replace
              the wild-card mapping with explicit 1:1 mappings, or add a
              reject_unverified_recipient restriction for that domain:

                  smtpd_recipient_restrictions =
                      ...
                      reject_unauth_destination
                      check_recipient_access
                          inline:{example.com=reject_unverified_recipient}
                  unverified_recipient_reject_code = 550

              In the above example, Postfix may contact a remote server if the
              recipient is rewritten to a remote 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
              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@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.

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
       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.

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.

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 parameter summary. See postconf(5) for more
       details including examples.

       canonical_classes (envelope_sender, envelope_recipient, header_sender,
       header_recipient)
              What addresses are subject to canonical_maps address mapping.

       canonical_maps (empty)
              Optional address mapping lookup tables for message headers and
              envelopes.

       recipient_canonical_maps (empty)
              Optional address mapping lookup tables for envelope and header
              recipient addresses.

       sender_canonical_maps (empty)
              Optional address mapping lookup tables for envelope and header
              sender addresses.

       propagate_unmatched_extensions (canonical, virtual)
              What address lookup tables copy an address extension from the
              lookup key to the lookup result.

       Other parameters of interest:

       inet_interfaces (all)
              The network interface addresses that this mail system receives
              mail on.

       local_header_rewrite_clients (permit_inet_interfaces)
              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_rewrite_domain parameter.

       proxy_interfaces (empty)
              The network interface addresses that this mail system receives
              mail on by way of a proxy or network address translation unit.

       masquerade_classes (envelope_sender, header_sender, header_recipient)
              What addresses are subject to address masquerading.

       masquerade_domains (empty)
              Optional list of domains whose subdomain structure will be
              stripped off in email addresses.

       masquerade_exceptions (empty)
              Optional list of user names that are not subjected to address
              masquerading, even when their address matches
              $masquerade_domains.

       mydestination ($myhostname, localhost.$mydomain, localhost)
              The list of domains that are delivered via the $local_transport
              mail delivery transport.

       myorigin ($myhostname)
              The domain name that locally-posted mail appears to come from,
              and that locally posted mail is delivered to.

       owner_request_special (yes)
              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 "-".

       remote_header_rewrite_domain (empty)
              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 ALSO
       cleanup(8), canonicalize and enqueue mail
       postmap(1), Postfix lookup table manager
       postconf(5), configuration parameters
       virtual(5), virtual aliasing

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

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

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



                                                                  CANONICAL(5)