sendmail, 4th Edition

Macros and the System Identity

The nature of email addresses requires that sendmail have a firm understanding of the machine on which it is running. The -d0.4 debugging switch (-d0.4 on page 542) causes sendmail to print its understanding of what the local machine is. A portion of that output displays the value of four key sendmail macros:

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

The short domain name (in $w; see $w on page 850) is simply the name of the local host without any domain information added as a suffix. The canonical domain name (in $j; see $j on page 830) is the fully qualified and official name of the local machine. The subdomain name (in $m; see $m on page 833) is just the domain part of the canonical name without a leading dot. And the node name (in $k; see $k on page 831) is the UUCP name of the local machine.

In addition to these macros, sendmail initializes the class $=w with a list of alternative names for the local host ($=w on page 876), and the class $=m with a list of the local domains ($=m on page 872).