This is really interesting! I remember the days when my fannish activity was mailing-list based, but in my case it was all book fandoms: the Mercedes Lackey list over at lists.herald.co.uk, all the Pern fandom lists, Sinnerstar's old George R.R. Martin mailing list. Probably others I'm forgetting. (I didn't really have TV access, so the concept of being fannish about a TV show--hell, the concept of a TV show; I thought they were just for news--was alien to me.)

A lot of book fandoms still are heavily mailing list based, if you're looking for gen discussion rather than fic. The Dragaera mailing list remains the only place I know with active discussion of Steven Brust's books, for example.