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.