I looked on my T-bird and can't find the backup function.
BTW, about two weeks ago I accidentally uninstalled T-Bird. Two days ago I reinstalled it and everything was still there. All the mail, contacts, etc.
I was happily surprised yet a bit confused. Why didn't the uninstall remove all that stuff?
Depends upon your operating system I would imagine.
Since I use Linux, this would work...
tar czvf thunderbird.20091209.tgz $HOME/.thunderbird
(Of course, I have a script to do this weekly. It also backs up my Firefox configuration)
If you use a less sophisticated operating system, you'll probably have to use other tools.
I was happily surprised yet a bit confused. Why didn't the uninstall remove all that stuff?
The program and the data are separate things.
You can remove the program without removing the data (i.e., messages and email account configs), and vice versa. I'd recommend that you determine what directory your email data and configs are in (hopefully you won't have to deal with a 'registry' -shudder), and back them up either by copying them to a different directory or drive, or archive them in a compressed file like I did above.