PoCoMy: Postfix + Courier + Mysql :: Webfrontend for administration. Features: Virtual domains, forwarding, aliases, sender aliases, multi user, multi language, privileges system, delegation of rights per domain, ...
MadMail is a simple Webmail client which can handle POP3, SMTP, and IMAP servers.
It is written with PHP (Sessions) an can displays HTML messages and MIME attachments.
Features multi-language support
No Database required