On Fri, 24 Jan 1997 11:13:43 EST, you said:
> From: Mail Delivery Subsystem <[log in to unmask]>
> 550 knuth.mtsy.edu (tcp)... Host unknown
> 550 bgmiller@knuth.mtsy.edu... Host unknown

<insert twilight zone theme here>

For what it's worth, there is a wildcard MX entry for 'mtsu.edu',
as follows:

mtsu.edu.       43200   MX      40 mail.uu.net.
mtsu.edu.       43200   MX      30 newsboy.isdn.net.
mtsu.edu.       43200   MX      20 acad1.mtsu.edu.
mtsu.edu.       43200   MX      10 frank.mtsu.edu.
mtsu.edu.       43200   MX      0 knuth.mtsu.edu.

Apparently, 'knuth' was down, 'frank' sucked up the mail, and then
bobbled it.  My guess is that somebody had a typo in /bin/hostname or
in the /etc/sendmail.cf (given that u and y are next to each other)

You might want to drop the postmaster a note, as it may take a while
for them to notice, if knuth is a pretty stable system - often the MX
secondaries may only have to actually DO sometning once every few
weeks.  At worst, they'll have already noticed and fixed it.  At best,
you'll have done your part to make the Internet safe for e-mail ;)

--
                                Valdis Kletnieks
                                Computer Systems Engineer
                                Virginia Tech