Re: post or reply by email
It sounds like this would be a great feature, except it raises some questions.
The first rule of a forum is search before posting. If a user was allowed to post new topics, there could be a lot of duplicate questions and threads. When a user replies to a message it usually gets some sort of “RE:” prefix by the email app, that could confuse the system. What about quoted text how would this be distinguished and eliminated? What if the user replied to questions inline, how would we know that? I am sure there are more, but those were the first to pop into my head.
I think if a reply and post feature is needed as a necessary part of your project you should look at a mail list manager. Is there an open source clone of google groups?