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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 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 re-
build 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 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.Last-
name, 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 be-
low.
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 $proxy_interfaces.
This form is useful for replacing login names by Firstname.Lastname.
@domain address
Replace other addresses in domain by address. This form has the lowest precedence.
Note: @domain is a wild-card. When this form is applied to recipient addresses, the
Postfix SMTP server accepts mail for any recipient in domain, regardless of whether
that recipient exists. This may turn your mail system into a backscatter source:
Postfix first accepts mail for non-existent recipients and then tries to return
that mail as "undeliverable" to the often forged sender address.
To avoid backscatter with mail for a wild-card domain, replace the wild-card map-
ping with explicit 1:1 mappings, or add a reject_unverified_recipient restriction
for that domain:
smtpd_recipient_restrictions =
...
reject_unauth_destination
check_recipient_access
inline:{example.com=reject_unverified_recipient}
unverified_recipient_reject_code = 550
In the above example, Postfix may contact a remote server if the recipient is
rewritten to a remote address.
RESULT ADDRESS REWRITING
The lookup result is subject to address rewriting:
o When the result has the form @otherdomain, the result becomes the same user in oth-
erdomain.
o When "append_at_myorigin=yes", append "@$myorigin" to addresses without "@domain".
o 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 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 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 con-
stituent 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 paren-
thesized 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_ta-
ble(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 mes-
sage headers from other clients at all, or rewrite message headers and update in-
complete 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 recipi-
ent_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)
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On Apache
Under GNU General Public License
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