Resetting Eudora settings without erasing vital mail server settings
Hold down ctrl and shift on the keyboard while going to Tools → Options. A dialog box will pop up asking you if you would like to reset your Eudora settings. This should reset all Eudora settings other than your mail server account options.
To reset your settings from within Eudora hold down the following modifier keys: Command + Option + Shift + Control. With your mouse select Special → Settings. A dialogue box should appear asking if you want to reset all but the most vital Eudora mail settings.