Lemmy is definitely different from how mailing lists work in practice - much faster to get updates on, more ergonomic, etc., but in theory - could SMTP, IMAP, and a bit of ingenuity be used to turn a mailing list into a Lemmy-like interface for comments, links, etc?

I just had the idea of making a mailing list-based ActivityPub host lol, but it would probably be much slower than Lemmy in just about every way because of protocol overhead.