> Mailing lists are kind of terrible beyond a certain point of complexity. First, they lead to a lot of self-spamming, with internal conversations.

This isn't a clear argument. What do you mean?

> So at very minimum, you want something threaded like email, but stored in a single location, so storage/duplication/deletion aren't problems

Certainly, the distributed nature of email may pose problems for an organisation which stores emails for a number of its employees. Storage is cheap and backup processes de-duplicate data so using mailing lists shouldn't pose too much difficulty.