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.
           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:

           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 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  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,  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:

           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 a ta-
           ble 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
           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 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 ($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 vir-
                  tual 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  list-
                  name-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.

    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)