Foedus Mail is a mail server written in Java that supports ESMTP, POP3, and IMAP. The project began in September 2002 because I was bored. Hopefully it will one day meet the criteria good software should (i.e. standards compliance, flexibility, simplicity, robustness, etc.).
Although there's a lot of working code already, half the trick right now is choosing what directions to move in. I intend to post the questions and challenges that come up along the way in places like the task manager, tracker, forum, etc., so feel free to make comments or suggestions at any time.