You say they are deleted. Do they show up in the Trash folder?

Are you using any other device such as another computer, a smartphone, a tablet etc, to view your messages?

Is it possible that Thunderbird is set to show only unread messages, so they become hidden out of sight after being read?

How can I turn off that feature that makes them hidden. I have tried emptying the trash. But they seem to disappear. Maybe they are in that other inbox folder. I have two of those.

Press Alt+v on your keyboard. Select messages on the menu and then the ALL entry.

Now I can not see the body of the text in the lower pane. I don't know how to fix that. Deanna

right click the folder and select properties and then the repair button.

This may well result in the mail actually disappearing, as a new index is built for what I think is now an empty file (it might not be)

If that is the case look in your anti virus program for what it did with the file inbox when it found a virus (or sent or whatever folder is a problem)