Ubuntu Manpage: aliascheck - check for existence of mail alias

NAME

       aliascheck - check for existence of mail alias

SYNOPSIS

       aliascheck [--nopwd] name [alias-file]

       aliascheck --map [--case] name map-file

       aliascheck --qmail [--nopwd] name [alias-user]

DESCRIPTION

aliascheck checks whether name is a valid email alias or a user in the password file. It
converts name to lower-case before performing any of the checks. If the alias or user
exists, aliascheck exits with status 0 and outputs what the address resolves to. If the
alias does not exist, aliascheck exits with status 1. If aliascheck cannot determine the
validity of name because of some system error, it exits with status 2.

aliascheck can run in three different modes--sendmail alias mode (the default), sendmail
map mode, and qmail mode. In sendmail alias mode the second argument, alias-file, is the
name of the sendmail alias file, typically /etc/mail/aliases.db. If no second argument is
supplied, aliascheck first checks for the existence of /etc/mail/aliases.db, then for the
existence of /etc/aliases.db, then finally exits with status 2 if neither file exists.
When an alias is found, aliascheck outputs the value of that alias in the alias database.

When aliascheck is invoked with --map, it looks up name in map-file, which should be a
database created with sendmail's makemap(8) utility. Note that maps have a slightly
different and incompatible format from that of alias files. Use the --case argument to
prevent name from being folded to lower-case before it is looked up in the database. Note
that --map implies the --nopwd option.

When aliascheck is given the argument --qmail, it runs in qmail mode. In this case, the
second argument, alias-user, specifies the user under which qmail processes mail aliases.
aliascheck will check this user's home directory for files named .qmail-XXX for various
appropriate suffixes XXX. On success, it outputs the full pathname of the appropriate
file.

If aliascheck cannot find an alias, it also checks the password file, and exits 0 if it
can find name there. If name is found, aliascheck also outputs name (in lower-case) to
standard output before exiting. (This is useful for Mail Avenger, because asmtpd does not
recognize users with invalid shells or UID 0, while MTAs typically do.) To suppress
password file checking, supply the --nopwd argument to aliascheck.

EXAMPLES

       If you are using Mail Avenger in conjunction with a sendmail installation, you might want
       to put the following code in your /etc/avenger/unknown file to reject mail for unknown
       users who do not show up in the alias file.

           aliascheck "$RECIPIENT_LOCAL" /etc/mail/aliases.db > /dev/null
           case "$?" in
               0)
                   # Fall through to default checks
                   ;;
               1)
                   reject unknown user
                   ;;
               *)
                   # Probably safest to do nothing, but could also
                   # defer the mail with the following command:
                   #
                   #defer Temporary error processing alias file
                   ;;
           esac

       If you have qmail instead of sendmail, assuming the qmail alias user is called "alias",
       you would change the first line in the previous example to:

           aliascheck --qmail "$RECIPIENT_LOCAL" alias > /dev/null

FILES

       /etc/avenger/unknown
           Mail Avenger rules for local email addresses that do not correspond to local users, or
           correspond to local users without valid shells, or local users with uid 0 (i.e.,
           root).  Note the location may be different if you set EtcDir in your asmtpd.conf file.

       /etc/mail/aliases.db
       /etc/aliases.db
           Default locations of sendmail alias file

       /etc/mail/virtusertable.db
           Default location of the sendmail virtual user table map, when this feature is in use.

       ~alias/.qmail-*
           Default locations of qmail alias files

       /etc/password
           System password file.  (Note, however, that aliascheck uses the getpwnam function, and
           will thus be compatible with schemes such as NIS that do not keep all users in the
           local password file.)

BUGS

       aliascheck doesn't necessarily know how to parse the particular database format your
       sendmail installation uses for aliases.  Make sure you test it before using it in an
       avenger script.

       In some sendmail installations, the alias database is not world readable, which can
       obviously prevent aliascheck from working properly if run under the wrong user identity
       (such as the AvengerUser).

       It is quite possible for aliascheck to return a system error (exit code 2), particularly
       if you run it while you are rebuilding a large alias database.  (aliascheck checks for the
       existence of special key "@" in the database.)  Make sure you differentiate between error
       code 1 (no user) and error code 2 (system error).

       aliascheck may not do the right thing if you installed qmail with conf-break set to a
       character other than "-".

       Remember that aliascheck does not read your qmail users/assign or users/cdb files--it only
       checks for .qmail files in the alias user's home directory.

AUTHOR

       David Mazieres