FossaMail is an email client built on the framework of Mozilla Thunderbird. However, unlike the Mozilla client, FossaMail is constantly supported by a team of developers. It is available in two versions: for 32-bit and 64-bit systems. FossaMail was created by the team behind the Pale Moon browser and has a minimalistic interface that differs slightly from Thunderbird in appearance. FossaMail is very stable and has its own built-in calendar and organizer. Additional functions include your own backup tool and address book.
FossaMail supports most add-ons made for Thunderbird. Plugin support looks weaker. The program is available for Windows starting with Windows Vista (Windows XP is not supported).