I am now using Outlook (imap). When I try to permanently delete a bunch of emails it deletes them and then I get a synchronizing inbox bar and the 1,000 or so emails come right back into my inbox. How do I avoid this if I am using Thunderbird?

Example: Have 9600 emails delete 2500 and notifies me that they will be permanently deleted but they never are. They just return a few minutes later. Thanks