Just a guess, but are you using some kind of filter to catch listserv commands before they go over the list. I'd like to know more about how that works. It looks like it just scans the first line and if it finds a listserv command, it bounces the message. Try starting the message with something like. "If you are ready to leave HISTARCH, you should send the following command to listserv ..." so that the words signoff and unsubscribe do not appear on the first line.