If you are using Evolution and are getting fed up of the little bugs and instabilities here and there then check out the article below on how to switch to Thunderbird:

http://maketecheasier.com/how-to-migrate-from-evolution-to-thunderbird-in-ubuntu-intrepid/2008/12/04

A quick highlight :

Migrate local mail from Evolution

First, we will migrate the Evolution mails that are stored locally in your hard disk.

Open up two Nautilus windows (if you like, you can open two tabs instead of two windows). Press Ctrl + H to reveal the hidden folders. In one window, navigate to the .mozilla-thunderbird folder. You should see a folder with name similar to i7bqvbzk.default. Click on that folder, followed by Mail and Local Folders. You should see some files like Inbox, Trash, Unsent Message etc.

In the second window, navigate to .evolution -> mail -> local folder. Similarly, you will find files such as Inbox, Outbox, Sent, Trash etc.

Now copy the five files Inbox, Outbox, Drafts, Templates, Sent from the Evolution folder to the Thunderbird folder. If it prompts you whether to replace the existing files, click Replace All.

If you have used any subfolders in your Evolution, you should see a folder with a .sbd extension (such as #evolution.sbd). In your Thunderbird folder, create a similar folder with the same name. Back to your Evolution folder, copy and paste all the files in the subfolder that don’t have a file extension to the Thunderbird subfolder.

That’s it. Restart your Thunderbird. You should see all your Evolution mails imported over.