July 15, 2004
Howard Rheingold writes in The Virtual Community (p. 77) that the first large mailing list on ARPANET was SF-LOVERS, for discussions about science fiction. A 1987 USENET post from the moderator of the list seems to be the best source on when the list started — around 1975. At that point, fewer than 100 hosts were online. It was nice of ARPA to allow users to put its network to literary uses then, almost 30 years ago.