I use Thunderbird for all of my email. Its easy to backup and move to another computer, and I love the anti-spam option.  In the past I’ve been able to backup and move Thunderbird from Linux to Linux and also Windows to Linux. I used these steps to get up and running quickly.

Note: I used Thunderbird 3.1.15 and Ubuntu Linux 10.04.

1) Install Thunderbird on the new computer and open Thunderbird once and then close it. This will create a profiles.ini and a folder with random letters followed with .default (Example: e9g849g8.default) in the.mozilla-thunderbird folder. Each profile is unique so let the computer create the file.

2) On the old computer find the Thunderbird folder (normally /home/username/.mozilla-thunderbird) and back up the entire folder. The .mozilla-thunderbird folder might be hidden, so you may have to enable Show Hidden Files, in the View menu.

3) On the new computer  copy the .mozilla-thunderbird folder from the old computer into your /home/username folder.

4) If should prompt you to merge the old folder with the new one. Make sure to select Merge All.

5) After the files are copied, open the .mozilla-thunderbird folder and you should see the new .default profile folder and the .default profile folder from the old computer.

6) Open the profiles.ini and change the Path from the new .default folder to the one you restored.

Example:

[General]
StartWithLastProfile=1

[Profile0]
Name=default
IsRelative=1
Path=e9g849g8.default

7) Once you have made the change, open Thunderbird, and voila! All your email and accounts should be setup and ready to go.

If you installed any plug-ins in your old system, you may need to install them and configure them, but its a small price to pay for getting everything back up and running so quickly.

I also recommend that you backup the entire .mozilla-thunderbird folder once a month. This way if the computer crashes and you need to reinstall, at least you wont have to start from scratch.