“LISTSERV” is the brand name of one kind of electronic mail-handling software for distributing messages to a list of subscribers. Other common brand names are “Majordomo” and “Listproc”. You can subscribe to the poodle-fluffing list, but not the LISTSERV. People at my university, where only Listproc is used, often (and erroneously) refer to themselves as managers of “listservs.” English teachers are frequently tripped up when typing “listserv” as part of a computer command; they naturally want to append an E on the end of the word. According to L-Soft, the manufacturer of LISTSERV, the name of their software should always be capitalized. See for the details.