Using classic Outlook for Windows in business environments
In the end I created a new Outlook profile with new Exchange accounts (instead of IMAP) - Exchange is the default and it re-synced all my email just fine. I then went back and deleted the old account files and the old profile after setting the new one to be the default - Start Outlook with the shift key on to manage profiles - why Microsoft seemed unable to offer such a simple solution is beyond me .....