man > canonical(5)

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 ad‐
       dresses. 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 a TCP-based server. In those cases, the
       lookups are done in a slightly different way as described below under "REGULAR EXPRESSION TA‐
       BLES" 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   re‐
       mote_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-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.

              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  solu‐
              tion.

       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  rewrit‐
              ten 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 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.

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.

       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  ad‐
              dresses  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  ad‐
              dresses.

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

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

       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_delim‐
              iter 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)