Updated: 2022/Sep/29
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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 a 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 addresses match
$masquerade_domains.
mydestination ($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)