    VIRTUAL(5)                                                          VIRTUAL(5)

    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:

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

           o      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  recipi-
                  ent 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 corre-
                  sponding 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, patterns are tried in the order as
           listed below:

           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:

           o      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.

           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 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@vir-
           tual-alias.domain as undeliverable.

           Instead  of  specifying  the  virtual  alias  domain  name via the vir-
           tual_alias_maps table, you may also specify it  via  the  main.cf  vir-
           tual_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 bro-
           ken 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 interpo-
           lated 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  con-
           stituent 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 propa-
                  gate  an  address  extension  from  the  original address to the
                  result.  Specify zero or more of canonical, virtual, alias, for-
                  ward, 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.

    SEE ALSO
           cleanup(8), canonicalize and enqueue mail
           postmap(1), Postfix lookup table manager
           postconf(5), configuration parameters
           canonical(5), canonical address mapping

    README FILES
           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)