I was just asked a few minutes ago to look into a problem with a Listserv
running on Windows 2000 that uses sendmail on a Freebsd Unix system for
its mail delivery services. The problem is that mail on the few lists on
this particular listserv, listserv.metanexus.net are not being distributed
to many subscribers. As of a few minutes ago, I have access to this Unix
box called cosmos.metanexus.net and the console is showing me messages
such as these:

/usr/share/misc/nslookup.help 93%May  8 22:20:04 orion sendmail[11167]:
f492Gak11167: ruleset=check_rcpt, arg1=<[log in to unmask]>,
relay=listserv.metanexus.net [192.76.184.64], reject=450 4.7.1
<[log in to unmask]>... Can not check MX records for recipient host HPU.EDU
May  8 22:20:04 orion sendmail[11167]: f492Gak11167: lost input channel
from listserv.metanexus.net [192.76.184.64] to MTA after rcpt
May  8 22:20:06 orion sendmail[11198]: f492K5k11198:
<[log in to unmask],>... Invalid route address

My suspicion is that the sendmail on the cosmos system is improperly
configured OR there's something wrong with the DNS entry for the system. I
am not sure of the specifics though. If anyone has any suggestions on what
exactly I should look at to solve this problem, please let me know.