The domaintable is generally used to force certain behavior after a DNS lookup has occurred. It permits the administrator to make shorthand names available for commonly referenced systems or domains by replacing the shorthand name with the proper one automatically. It can also be used to replace incorrect host or domain names with the ``correct'' information.
Most sites will not need any domaintable entries.
The following example shows how to replace an incorrect address people are attempting to mail to with the correct address: