Ubuntu Manpage: virtual - Postfix virtual alias table format

Provided by: postfix_3.3.0-1ubuntu0.4_amd64

NAME

       virtual - Postfix virtual alias table format

SYNOPSIS

       postmap /etc/postfix/virtual

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

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

DESCRIPTION

The optional virtual(5) alias table rewrites recipient addresses for all local, all
virtual, and all remote mail destinations. This is unlike the aliases(5) table which is
used only for local(8) delivery. Virtual aliasing is recursive, and is implemented by the
Postfix cleanup(8) daemon before mail is queued.

The main applications of virtual aliasing are:

• To redirect mail for one address to one or more addresses.

• To implement virtual alias domains where all addresses are aliased to addresses in
other domains.

Virtual alias domains are not to be confused with the virtual mailbox domains that
are implemented with the Postfix virtual(8) mail delivery agent. With virtual
mailbox domains, each recipient address can have its own mailbox.

Virtual aliasing is applied only to recipient envelope addresses, and does not affect
message headers. Use canonical(5) mapping to rewrite header and envelope addresses in
general.

Normally, the virtual(5) alias 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/virtual" 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
case, the lookups are done in a slightly different way as described below under "REGULAR
EXPRESSION TABLES" or "TCP-BASED TABLES".

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, 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, address, ...
Redirect mail for user@domain to address. This form has the highest precedence.

user address, address, ...
Redirect mail for user@site to 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 functionality overlaps with functionality of the local aliases(5) database.
The difference is that virtual(5) mapping can be applied to non-local addresses.

@domain address, address, ...
Redirect mail for other users in domain to address. This form has the lowest
precedence.

Note: @domain is a wild-card. With this form, 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.  This works only for the  first  address  in  a  multi-address  lookup
              result.

       •      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.

VIRTUAL ALIAS DOMAINS

Besides virtual aliases, the virtual alias table can also be used to implement virtual
alias domains. With a virtual alias domain, all recipient addresses are aliased to
addresses in other domains.

Virtual alias domains are not to be confused with the virtual mailbox domains that are
implemented with the Postfix virtual(8) mail delivery agent. With virtual mailbox domains,
each recipient address can have its own mailbox.

With a virtual alias domain, the virtual domain has its own user name space. Local (i.e.
non-virtual) usernames are not visible in a virtual alias domain. In particular, local
aliases(5) and local mailing lists are not visible as localname@virtual-alias.domain.

Support for a virtual alias domain looks like:

/etc/postfix/main.cf:
virtual_alias_maps = hash:/etc/postfix/virtual

Note: some systems use dbm databases instead of hash. See the output from "postconf -m"
for available database types.

/etc/postfix/virtual:
virtual-alias.domain anything (right-hand content does not matter)
postmaster@virtual-alias.domain postmaster
user1@virtual-alias.domain address1
user2@virtual-alias.domain address2, address3

The virtual-alias.domain anything entry is required for a virtual alias domain. Without
this entry, mail is rejected with "relay access denied", or bounces with "mail loops back
to myself".

Do not specify virtual alias domain names in the main.cf mydestination or relay_domains
configuration parameters.

With a virtual alias domain, the Postfix SMTP server accepts mail for
known-user@virtual-alias.domain, and rejects mail for unknown-user@virtual-alias.domain as
undeliverable.

Instead of specifying the virtual alias domain name via the virtual_alias_maps table, you
may also specify it via the main.cf virtual_alias_domains configuration parameter. This
latter parameter uses the same syntax as the main.cf mydestination configuration
parameter.

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 to this topic. See the Postfix
       main.cf file for syntax details and for default values. Use the "postfix  reload"  command
       after a configuration change.

       virtual_alias_maps
              List of virtual aliasing tables.

       virtual_alias_domains
              List  of  virtual  alias  domains.  This  uses the same syntax as the mydestination
              parameter.

       propagate_unmatched_extensions
              A list of address rewriting or forwarding  mechanisms  that  propagate  an  address
              extension  from  the  original  address  to  the  result.   Specify zero or more of
              canonical, virtual, alias, forward, include, or generic.

       Other parameters of interest:

       inet_interfaces
              The network interface addresses that this system receives mail  on.   You  need  to
              stop and start Postfix when this parameter changes.

       mydestination
              List of domains that this mail system considers local.

       myorigin
              The domain that is appended to any address that does not have a domain.

       owner_request_special
              Give special treatment to owner-xxx and xxx-request addresses.

       proxy_interfaces
              Other  interfaces  that  this  machine  receives mail on by way of a proxy agent or
              network address translator.

README FILES

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

                                                                                       VIRTUAL(5)