This reminds me of Zoe. http://zoe.sourceforge.net

Back in 2001 or 2002, I was following the progress of Zoe, what I thought to be a very promising new approach to email archives. It kept your email in mbox or eml files, used Lucene for indexing and search and then provided a web interface on an embedded web server.

The Zoe project is no longer active (the homepage is dead and the files are gone), but this MailPile sounds very much like it. Almost exactly like it. I hope it does better.