I don't use emacs, but have you considered something like Discourse (usable/postable as a mailing list + a proper modern forum for the less email liking)? Posts can also be made 'community wikis' and have revision history.

We'll actually be switching to Discourse soon :) Believe me, I am no fan of Google Groups.

I didn't know that Discourse had community wikis. Then we can switch off of GitHub too (plus, git is a bit heavyweight for what is essentially a wiki doc :) )