>Just out of curiousity, how does listserv, or any given server, determine >whether or not such a user exists? What sort of occurence could generate >these spurious error messages? LISTSERV operates on the assumption that when a host says the user is unknown, the host is telling the truth :) This is why probing and not using hair-trigger auto-deletes is probably the best way to go. At least if you probe someone for several days and the probe fails you have a fair amount of certainty that the user is actually gone. I have no idea what could cause a server to tell you that a user is unknown when he actually exists. I suppose there are probably all kinds of reasons for it, mostly due to configuration errors and other system problems on the user's host. Nathan