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.  These tables
       are often queried with a full email address (including domain).

       This is unlike the aliases(5) table (alias_maps) which applies only  to
       local(8)  recipients. That table is only queried with the email address
       localpart (no domain).

       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 are often searched with a full email
              address (including domain) and that  apply  to  all  recipients:
              local(8),  virtual,  and  remote; this is unlike alias_maps that
              are only searched with an email address  localpart  (no  domain)
              and 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)