Question to the Fediverse:

I'm looking for a mailing list / newsgroup solution (it can be SaaS or self hosted).

I need a couple things:
- Easy subscribe and unsubscribe functions
- Ability to send out mass emails to subscribers (basic functionality)

- Most important... and this is the weird part... I need all the subscribers to be able to "reply all" or to email the list as a whole, to also send messages to everyone. But I don't want them to be able to see everyone on the list.

I need an oldschool mailing list proper, where people can track the threads and replies, right.

All the marketing email lists are only top-down - the emailer mails all the recipients, but there is no allowing the recipients to email each other.

The best I have found is GNU MailMain: https://www.gnu.org/software/mailman/

Does anyone know any other examples?

Edit to add better nomenclature (my brain is not forming words right now):
- Allows for email discussion
- Allows for email threading
- Email Newsgroup - that's a good one

Editing to add answers to my own question:
- GNU Mailman: https://www.gnu.org/software/mailman/
- Gaggle Email: https://gaggle.email (cheers @zebbm)
- Groups io: https://groups.io (cheers @TNLNYCTristan Louis )
- Gray Duck Mail: https://grayduckmail.com
- mlmmj: https://mlmmj.org