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VIRTUAL(5) File Formats Manual 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:

  • To redirect mail for one address to one or more addresses.
  • 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 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:



  

  
When pattern matches a mail address, replace it by the
      corresponding address.

  

  
Empty lines and whitespace-only lines are ignored, as are lines whose
      first non-whitespace character is a `#'.

  

  
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.



  

  
Redirect mail for user@domain to address. This form
      has the highest precedence.

  

  
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:


    
  
  • 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.
    • 
  
  • When "append_at_myorigin=yes", append
      "@$myorigin" to addresses without
    "@domain".
    • 
  
  • 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 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@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 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
    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 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 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.



  

  
Optional lookup tables with aliases that apply to all recipients:
      local(8), virtual, and remote; this is unlike alias_maps that apply
      only to local(8) recipients.

  

  
Postfix is the final destination for the specified list of virtual alias
      domains, that is, domains for which all addresses are aliased to addresses
      in other local or remote domains.

  

  
What address lookup tables copy an address extension from the lookup key
      to the lookup result.




Other parameters of interest:



  

  
The local network interface addresses that this mail system receives mail
      on.

  

  
The list of domains that are delivered via the $local_transport mail
      delivery transport.

  

  
The domain name that locally-posted mail appears to come from, and that
      locally posted mail is delivered to.

  

  
Enable special treatment for owner-listname entries in the
      aliases(5) file, and don't split owner-listname and
      listname-request address localparts when the recipient_delimiter is
      set to "-".

  

  
The remote 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




Use "postconf readme_directory" or
    "postconf html_directory" to locate this information.


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