I recently restored an old c:\ drive image while I was trying to find a more recent one.
On this old c:\ drive I had The Bat v. 1.61.
I loaded it up and it read all of my accounts correctly, but of course could not send/receive messages because
of an expired certificate problem.
After it had read all the messages, one account's Outbox showed approx.
500 messages and the number was in bold.
Fast forward to now. I have just found and restored a much newer image, with The Bat v. 4.2.36 on it.
When I load The Bat now, it too is showing a bolded
500 for this same Outbox folder.
None of the messages in the folder are un-read.
Would anyone know how to right this situation?
....
Well I just deleted all of these messages and that solved the problem!

Not sure how all those messages ended up in that folder.