It sounds like LISTSERV might not be able to resolve the address of your mail server. Please check the SMTPS#1-yymmdd.LOG files to see if there's any indication of this (e.g., "Can't resolve MAIL.ECONOPHONE.COM - will try again in one minute"). There may be a DNS problem that isn't evident when you send mail via your mail client. Also, if MAIL.ECONOPHONE.COM is set to reject "relayed" mail, I can see how this might be happening. Nathan