You'd have to look in the log to see what userid is actually being seen by LISTSERV. I'm guessing it's looking at whatever is in the Sender: field and that the Sender: field doesn't have a fully-qualified address in it, but without more information it's practically impossible to say. The bottom line is that whatever address is in the To: line of LISTSERV's response isn't valid (probably because it's not syntactically correct). Nathan