When you click on mouse or use 'Delete' key on keyboard, the keyboard (or mouse) communicates with computer a specific instruction. Computer understands communication and carries out the event as described in the program code - eg: Delete the selected item.

If the program code was not correct then it would be failing in all delete methods and the Thunderbird forum would be inundated with people with same problem, which is not the case, so this cannot be a problem with the actual code for 'Delete'.

Can you offer a bit more info to understand the process you are using? Do you have the Message Pane enabled or not? Do you usually open email in a tab?

Do you have focus within the email itself in Message Pane - you have clicked somewhere within the message itself - when you use keyboard 'Delete' key ? OR have you just clicked on email in Thread Pane so focus is still in the Thread Pane list - it is still a strongly highlighted as selected - when you use 'Delete' key?

Do you use the 'Threaded' option ? Is the selected email threaded, but is a collapsed thread ? So in effect you end up deleting the thread, not just a single email?

Here is a screen cap of how I use it. If I click on your email from Moz, both those emails will be deleted. Well most of the time anyway. sometimes it does just delete one. Thanks for trying to help!!!

Uninstalled Thunderbird with an uninstaller program and reinstalled. It seems to be working again! Thanks for trying to help!