http://kb.mozillazine.org/Update_an_obsolete_version_of_Thunderbird

Support for Mac OSX 10.4 and the PPC platform (G3, G4, G5) was dropped in Thunderbird 5.0.

https://website-archive.mozilla.org/www.mozilla.org/thunderbird_releasenotes/en-us/thunderbird/5.0/system-requirements/

The release prior to 5 was 3.1 https://website-archive.mozilla.org/www.mozilla.org/thunderbird_releasenotes/en-us/thunderbird/3.1/releasenotes/

Old versions here http://ftp.mozilla.org/pub/thunderbird/releases/

Thank you for your quick reply ... I will pass the information along to my friend.

Apple hardware made before 2012 was of the highest quality and not crippled or limited in any way ... so an incredible number of these systems are still working quite well - and ALL can be converted to some version of Linux if you try.

The LATEST M1 Apple hardware WON'T Run anything Except Apple approved OS / and Applications: and is a Real jail locking you into Apple's Will ... they CAN alter your system without your consent ... you don't really OWN your computer any more. Same thing for Windows 11 ... you can only boot what Microsoft SAYS you can boot. Antique Computers for ME / OR Build my Own - FOREVER!!!!

So, all things considered, I do not blame my friend for using the same computer for 16 years. That G5 just got a new video card: so it should be good for another 16 years. And this fact means that there will always be a real and valid use for the Thunderbird release archive (And you incredible Support volunteers!). Thank you!

(He is new to Thunderbird ... it is installed on half of his computers already. Now it will be his mail client on 3/4 of his computers!)

I just replaced my 2012 Dell computer. So I understand. But I am also reluctant to put ancient software on the internet. This is why https://www.mozilla.org/en-US/security/known-vulnerabilities/thunderbird/#thunderbird91.9 No one is fixing the old stuff.