T-dah is a free PHP webmail application which is built from the well-known Uebimiau script & offers a slick interface.
It can be up & running in a few minutes on any PHP (4 or 5) enabled server as no database is required.
The application uses the POP3 protocol & can be configured to use SMTP, PHP mail, Sendmail or Qmail for sending e-mails.
XMail Server Lite is an open source & free mail server with an Ajaxed webmail bundled to it.
It is compatible with Window & Linux OSs with 2 different installers provided.
The server is capable of managing SMTP/ESMTP & POP3 protocols with web-based administration panel.
It supports unlimited domains/users including virtual domains & aliases.
conjoon is a web-based open source application, built with the Zend Framework, that focuses on message exchanging.
Currently, it is a full-featured webmail & RSS reader client with contacts management. But the upcoming releases show that it will also have an integrated Twitter client with multiple accounts support.
Xeams is a free e-mail server software that supports POP3, SMTP, IMAP & works in all major operating systems (Windows, Linux, Solaris, MacOSX).
It comes with a powerful spam engine which can stop most of them by default & lets you to customize the rules further.
The server is controlled from a web-based interface which also helps you to live-monitor the system.
It has support for detailed logging, mailing lists, customized footers & much more.
Roundcube is an open source webmail application with a slick, desktop-like interface.
It is multilingual (already comes with 60+ languages) and offers most of the functionality you can expect from a webmail like:
Messages can be managed with drag’n drops, users can have multiple sender identities and it can work with unlimited users/messages.
