I know some of the MAIL implementations were evaluated. However, I don't remember GNU JavaMail as being one of them.
http://www.gnu.org/software/classpathx/javamail/ It claims to implement JavaMail 1.3 specifications and has SMTP, IMAP4rev1, POP3, mbox and Maildir support. It is released under GPL. If it was already mentioned, ignore the email. Bilal
