Delete a Message Bypassing the Trash
Normally when you click the delete button, the email message goes to the Trash folder and sits there until you manually empty the trash, or until it’s automatically deleted, depending on your settings. (Look in Account Settings > Server Settings and Message Storage to see how yours is set up.)
To immediately and irrevocably delete a message in Mozilla Thunderbird, Netscape, or Mozilla:
Open the email client. Select the message you want to delete in the message list (without opening it). Hold down the Shift key while pressing Del. In the Confirm Deletion box, press Delete. Your message will be deleted immediately, and no copy will be saved to the Trash.
