Ubuntu Manpage: virtual - Postfix virtual alias table format

Provided by: postfix_3.9.1-10ubuntu1_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 (virtual_alias_maps) applies to all recipients: local(8), virtual,
and remote. This feature is implemented in the Postfix cleanup(8) daemon before mail is queued.

This is unlike the aliases(5) table (alias_maps) which applies only to local(8) recipients.

Virtual aliasing is recursive; to terminate recursion for a specific address, alias that address to
itself.

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 a 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 the 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.

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 aliased 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.  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 a 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  available  in
       Postfix 2.5 and later.

       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 ($virtual_maps)
Optional lookup tables with aliases that apply to all recipients: local(8), virtual, and remote;
this is unlike alias_maps that apply only to local(8) recipients.

virtual_alias_domains ($virtual_alias_maps)
Postfix is the final destination for the specified list of virtual alias domains, that is, domains
for which all addresses are aliased to addresses in other local or remote domains.

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 local network interface addresses that this mail system receives mail on.

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 "-".

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

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)