I don't get it, email is the easiest thing in the world to backup and view offline. You can just run e.g. offlineimap to periodically download the messages, and then you can use virtually any email client to view them

Tracking replies is done automatically as long as you actually click "reply", because mail clients add the In-Reply-To header with the ID of the message you're replying to.

I'm not trying to be obnoxious, I just don't understand what's the issue.