Using Mozilla Thunderbird over other email applications is mostly a matter of preference. However, the fact that it is an application that runs on Windows, OSX and GNU/Linux is a very big reason for using it rather than other similar applications. Not only is it running on these operating systems, but it is extremely easy to move your mail and all of your settings to another computer and/or operating system.
I discovered this after temporarily moving one of my sisters onto my G5 after her Windows machine stopped booting. I was able to use the Ubuntu 6.06 live cd to access her hard drive and copy all of her important documents to my iPod Mini.
The files you need to retrieve from the Windows PC are in the following directory:
Documents and Settings/
<username>/Application Data/Thunderbird/Profiles/xxxxxx.default/
These are the files you need from there:
Address Book: abook.mab
Preferences: prefs.js
Mail: Mail (folder/directory)
It is probably also a good idea to go to Address Book while in Thunderbird and export your addresses to one of the more universal formats like ldif or csv. I won’t make any promises if you try to import them to another email application, but you can at least open those with a spreadsheet application if all else fails.
Keep those files in a safe place or back them up along with anything else that’s important to you. Now go to the new machine or go ahead and install another operating system, whatever. On the new system install Thunderbird and then load it and walk through the account set up with some dummy info. I do this so that when I go into the directory to find the place for my old files to go there’s something there for me to replace. It also reaffirms that I am putting them in the right place.
Close Thunderbird after you finish the account set up. In your file browser find your Thunderbird files. Following are locations for those files in different OSs to the best of my knowledge:
OSX:
HD/Users/<username>/Library/Application Support/Thunderbird
Windows:
C:/Documents and Settings/<username>/Application Data/Thunderbird
Ubuntu:
/home/<username>/.mozilla-thunderbird
(Most Linux OSs will be similar. Note that .mozilla-thunderbird is a hidden file. In most Linux file browsers there is an option under ‘View/Show Hidden Files’.)
Okay, now all you have to do is copy your old files to this directory and in doing that you will replace or overwrite the existing files:
Address Book: abook.mab
Preferences: prefs.js
Mail: Mail (folder/directory)
Once that is done, load Thunderbird and it should look like you never left home!
I am offering these instructions to be helpful. By attempting to do this you are accepting all responsibility for the outcome. I cannot guarantee success. Make sure that you take notes on any information regarding access to your mail servers and accounts before deleting your existing Thunderbird set up.