Open WebMail is a webmail system designed to manage very large mail folder
files in a memory efficient way. It also provides a range of features to help
users migrate smoothly from Microsoft Outlook to Open WebMail. Open WebMail
has the following features: multiple languages, multiple iconsets/styles,
strong MIME support, virtual host/login alias, PAM support, online password
changing, convenient folder/message operations, draft folder, confirmed
reading support, full content search, a spelling checker, auto reply, mail
filtering, POP3 support, and message count previewing.

WWW: http://openwebmail.org/