CUNY Academic Commons

The way post by email works is you set the from email address in the blog/site settings and only email from that address can post. That method wouldn't work here. In addition to the parsing, you would need a key hashing and recognition system (similar to activation keys) to attach replies to the correct user, thread & post.

I don't think the post by email core plugin had much traction. The codex page says it needs updating, but that may be because some filters and constants were added in 3.0.

http://codex.wordpress.org/Post_to_your_blog_using_email