This term looks like it's missing an "e", but that's how it's spelled. A listserv, or list server, is a small program that automatically sends messages to multiple e-mail addresses on a mailing list. When someone subscribes to a mailing list, the listserv will automatically add the address and distribute future e-mail messages to that address along with all the others on the list. When someone unsubscribes, the listserv simply removes the address. At least that is the way it supposed to work. Unfortunately, with some SPAM lists, unsubscribing only adds you to more lists.