    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 (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:

           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  with aliases that apply to all recipi-
                  ents: 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 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 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  list-
                  name-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 transla-
                  tion 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)