Mail Server

Postfix - Postfix is an alternative to Sendmail, developed by Wietse Venema and maintained by Google. It runs on various UNIX-like systems and offers source code distribution, documentation, mailing lists and more.

Roundcube is a web-based IMAP email client. It makes extensive use of Ajax technology. Roundcube is licensed under the GNU GPL version 3 or later, with exceptions for skins and plugins. Wikipedia