Ubuntu Manpage: virtual - Postfix virtual alias table format

Provided by: postfix_3.8.6-1build2_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. This feature is implemented in the Postfix cleanup(8)
daemon before mail is queued.

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 that alias specific mail addresses or domains to other local
or remote addresses.

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 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 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)