Apple Mail - Duplicate Mail Issues

I've been using Apple Mail for decades. I have mailboxes that have only had a dozen emails in them now showing over 30,000 of the same emails. I try to remove them manually but they always come back. They are all IMAP mails on a private server.

Apple Mail is the most neglected app from Apple, and has major issues now.

Any suggestions on how to permanently remove these false emails?