Claws Mail

Website/Download: http://www.claws-mail.org/
License: Freeware
OS: Windows Linux
Latest Version: 3.7.2
Publisher's description:
Claws Mail is a free, GTK+-based, open source email and news client. It offers easy configuration and an abundance of features. It stores mail in the MH mailbox format and also the Mbox mailbox format via a plugin. Claws Mail runs on both Windows and Unix-like systems such as Linux, BSD, Solaris, and Mac OS X.