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.