FossaMail

I've been trying this out; it's very similar to Thunderbird and works very well. From the homepage

Quote:

FossaMail is an Open Source, Mozilla Thunderbird-based mail, news and chat client for Windows and Linux, brought to you by the Pale Moon developers (and therefore not affiliated with the Mozilla Corporation). It is an alternative version of the Mozilla Thunderbird mail&news client, and based on the Pale Moon browser core.

If you want to try it out, you can get more info and a download link here:

FossaMail

If you already use Thunderbird, there's a tool you can get to migrate your profile (addresses, accounts, emails) to FossaMail. As FossaMail has a separate profile to that of Thunderbird, you can run both programs if you wish to. There's also a backup tool available.

FossaMail Profile Migration Tool

FossaMail Profile Backup Tool

There's an add-on, called Lightning, which is a calendar and organiser, incorporated into Thunderbird and you can get the same thing in FossaMail. Be sure to get it from the same place where you download FossaMail from, because if you get the Thunderbird version of the add-on, it won't work.

FossaMail has its own forums on the Pale Moon forum site here:

Pale Moon forum • View forum - FossaMail

FossaMail