I can empty the Trash of emails

What exactly are you doing?

The emails themselves will empty. If you look at my attached photos, the empty folders that I am done using and are empty, won’t delete, and won’t go away. There’s no content inside the folders.

Just my guess, but those look like server side folders that the server might not be prepared to function without. (deleted message and send messages)

Today I looked and the folders were gone. I did nothing. I have no explanation. Maybe it is a server thing as stated by Matt. THANKS to those on Mozilla Support!