From what I heard of VMSHARE, HPO 5.0 simply doesn't work. "If you plan to install HPO 5, please locate the nearest brick and hit yourself hard on the head. You will find it to be a much more productive use of your time" (that's probably not the exact quotation but I think it's close enough). So the issue of whether or not LISTSERV will work under HPO 5.0 is a bit academic :-) Eric