outlook eudora thunderbird

You need to let everyone know what version of windows you are running any time you need help with a problem.

In XP, in the right pane, under the Control Panel icon, you should see Set Program Access and Defaults, have you changed your email program there?

You might also need to install Eudora again, then run Revo Uninstaller to be sure it has been completely removed from your computer.
Revo http://majorgeeks.com/Revo_Uninstaller_d5706.html

Notes for using Revo so you do not make your computer unbootable!
1. Keep the default setting (moderate removal).
The software will use the program's own uninstaller, provided there is one.
But, it also does an additional step of finding all the useless registry entries left behind.
2. If the program's uninstaller tells you that you need to reboot, hit cancel because Revo has not finished the job. If you do reboot, Revo can't finish a good cleanup.
3. When Revo presents you with a tree of registry entries, DO NOT click the delete all button. This would remove entries that windows needs to boot properly.
You only select the entries that are in bold. Put a check/tick in the boxes in front of the bolded items then choose delete selected.