JWebMail
WebMail is a www-frontend to IMAP/POP3 mailboxes. You can compare it to the systems Hotmail, YahooMail etc use. It allows a user to access his mailbox via the world wide web and do most things other mail programs allow to do, even if he is not sitting on his own personal computer or corporate LAN.
(追記) (追記ここまで)
License
GNU Library or Lesser General Public License (LGPL)