[thaumasiotes]

I'm open to correction, but I believe it's essentially a bunch of email lists. You can post to rec.games.roguelike.angband, your message will go to a server somewhere (theoretically, to every Usenet provider), and people who want to discuss, or read discussion of, Angband, can ask that server for the set of messages associated with rec.games.roguelike.angband.

So email, if you sent mail to topics rather than to recipients.

[usrusr]

I've always assumed (never looked into it) that the protocol itself has little in common with SMTP. But the constraints of text-only messages (email before html formatting took hold), email address as user ID and client software that used the same UI for both (Netscape Navigator!) certainly made it feel like very much the same thing. Mailing lists, but more federated than irc.

One difference to mailing lists of more recent times, besides technological differences, is that there was more of a sense of shared culture across groups. Groups certainly differed (some topics might have even had parallel groups in regular and in alt.* hierarchies?), but not even remotely as much as mailing lists differ. Certainly more free for all babble (because it was) than the more moderated or even announcement-only end of the mailing list spectrum that is enabled by their centralised nature.

[SyberShock]

Usenet runs on the NNTP protocol. NNTP stands for "Network News Transfer Protocol." It is not a mailing list but many mailing list operators mirror their mailing lists in a NNTP newsgroup. This is done with a mail-to-news gateway script.

Usenet is typically accessed with a news reader application like Thunderbird. Thunderbird is not just a email client. It is also a news client that allows you to subscribe to and post to newsgroups.