In a nutshell: migrate https://lists.wikimedia.org from Mailman to Discourse, including archives, providing email-based and web-based features, as well as public and private channels.
Hi @revi, good point. I *think* Discourse doesn't do this out of the box, but we can investigate (and probably discuss in a task apart). Maybe a plugin exists. If not, I guess a plugin to have posts deleted automatically after N time wouldn't be too far apart from existing functionality. Currently it is possible to *close* topics automatically in a specific category after N time.
Well, yes, I was about to ask why. :) In Discourse entire topics (threads) or specific posts (messages) can be deleted by admins and moderators from the web UI. There is also an API for that.