Mozilla Thunderbird is a redesign of the Mozilla mail component. The goal is to produce a cross platform stand alone mail application using the XUL user interface language. The intended customer is someone who uses Mozilla Firefox (or another stand alone browser) as their primary browser and wants a mail client based on mozilla that "plays nice" with the browser.
Reviewing 15.0.1 (Sep 12, 2012)
still one of the best mail clients you can get. although hardly anyone uses non-webmail these days. if you are going to do it use this!
Reviewing 3.0 Final (Dec 8, 2009)
As a long time version 3.0 beta tester, I'm glad to see it reach the final version.
The search everywhere is a good feature and there is a switch to let Spotlight search messages. The combined inbox is useful and the migration tool takes care of that. Integration with Mac OS X isn't seamless, but the Mac OS X Address Book can be accessed in the Address Book list.
The migration tool made a security change which may or may not annoy: it wanted me to use a master password and each time you start the browser it asks for that password.
A sticking point for me is that the Lightning extension is still in beta test and wasn't ready for use with Thunderbird version 3.0.
Reviewing 3.0 RC1 (Nov 24, 2009)
Better than Mail.app
Reviewing 22.214.171.124 (Jun 2, 2006)
Best simple home mail client, bar none.
Reviewing 1.0.7 (Sep 30, 2005)
Pretty solid - not bad at all.
Wish it would do on the fly spell checking like Apple Mail does, and also had the same kind of right-mouse button menu options as Apple Mail does (look up in dictionary, look up in google, etc.)
It does have newsgroup support, but I do wish it allowed you to set it so it did not abbreviate newsgroup names.
Still, all in all, so far, so good.
mozilla have put out a great product here. even in 2012 this is a very handy email client.