sendmail, 4th Edition

Make sendmail DNS-Aware

Not all releases of sendmail are ready to use DNS. To determine whether yours is ready, type the following command:

% /usr/sbin/sendmail -d0.1 -bt < /dev/null
Version 8.14.1
 Compiled with: LOG MIME8TO7 NAMED_BIND NETINET NETUNIX NEWDB SCANF
                USERDB XDEBUG

=  ==  ==  ==  ==  ==  = SYSTEM IDENTITY (after readcf) =  ==  ==  ==  ==  ==  =
      (short domain name) $w = here
  (canonical domain name) $j = here.uofa.edu
         (subdomain name) $m = uofa.edu
              (node name) $k = here
=  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==  ==
 ==  ==  ==  ==  ==  ==  =

Look for a statement that indicates whether your sendmail was compiled with NAMED_BIND support (NAMED_BIND on page 124). If it was, it can use DNS. If it wasn’t, either you will have to get a corrected version from your vendor, or you will have to download and compile the latest version of sendmail from scratch (Download the Source on page 42).

But even if your sendmail binary supports DNS, site configuration might not. If your host supports a service-switch file, for instance, make sure that file lists dns as the method used to fetch information about hosts.

If your sendmail still seems unable to use DNS, despite your efforts, look for other reasons for failure. Make sure, for example, that your /etc/resolv.conf file is present and that it contains the address (not the name) of a valid name-server machine for your domain.