# Postfix manual - virtual(5)

    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   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 expres-
           sions,  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 result
                  When pattern matches a mail address, replace it  by
                  the corresponding result.

           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  logi-
                  cal 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 $mydes-
                  tination, 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 recip-
           ient 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 propa-
           gated 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 vir-
           tual 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 ta-
           ble, 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 descrip-
           tion 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
           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 mecha-
                  nisms 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 Post-
                  fix 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 transla-
                  tor.

    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

                                                                        VIRTUAL(5)