I am not sure why this happened, but one likely possibility is that there is a very small amount of people using one of the two types of headers you mentioned (most subscribers usually get short headers). While going through the DISTRIBUTE process, LISTSERV@AKRONVM might realize that you are the only recipient down the path and mail directly to you, ie through its local mailer, to save cycles and bandwidth. With the other type of header there might be 10 other people down that path and the DISTRIBUTE process will continue normally. Eric