Article 6100 of comp.protocols.tcp-ip.domains:
Path: mri.com!news.aimnet.com!netserv.com!news.clark.net!news.sprintlink.net!news-dc-2.sprintlink.net!newsfeed.internetmci.com!news.msfc.nasa.gov!elroy.jpl.nasa.gov!decwrl!waikato!auckland.ac.nz!news
From: Daymon Nin <d.nin@auckland.ac.nz>
Newsgroups: comp.protocols.tcp-ip.domains
Subject: RE: MX records - this _must_ be possible...
Date: 11 Jun 1996 00:16:52 GMT
Organization: University of Auckland
Lines: 25
Distribution: inet
Message-ID: <01bb572b.5a6ca360$e1c1d882@tmk105.tmk.auckland.ac.nz>
References: <4p4laq$qjk@skat.usc.edu> <sreybm2yn8t.fsf@ptavv.nersc.gov> <4p74ds$o94@skat.usc.edu> <4pa87g$60d@flash.noc.best.net>
NNTP-Posting-Host: w.turner.tmk.auckland.ac.nz
X-Newsreader: Microsoft Internet News

If you have sendmail 8.7, you can use a mailertable to do this:

create a file /etc/mailertable, and add the following line to it:

domain.com:	local:[alpha.domain.com]

then build a hashed version of it:

makemap hash /etc/mailertable.db < /etc/mailertable

Then define the mailertable in the site.mc file, with

FEATURE(mailertable)   --- This assumes mailertable.db will be in /etc,
and in hash format

The advantage of doing it this way, is that you don't need to rebuild your
sendmail.cf file, or restart sendmail if you add additional hosts inside
your domain, and want to have mail forwarded to those hosts.

Using the []'s around the host name prevents sendmail from using BIND to
find the mail exchanger for it.

-Daymon Nin