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

Mail Avenger 0.8.4                                 2013-07-13                                      aliascheck(1)