Can anyone point me in the right direction, regarding this problem I can send e-mails from the server. But when a test user tries to subscribe to a listserv They do receive a confirmation e-mail. their subscription does not get activated until they respond to the e-mail. When the e-mail reply is sent, the Exchange server claims the recipient is unknown. (The machine that is hosting the listserv is internally lurch.prod.oclc.org and externally is called www.sitesearch.oclc.org and sitesearch.oclc.org) I think the probem may be with the Exchange server's aliases file? the logs I have of the transaction are below (I tried this with the listserv aliases and with an existing user "Summanen" on the server) sendmail is getting no errors (neither is the listserver software (mailman)). I have no access the exchange server so I cannot track the error response any closer...:(