I'm also having issues with the new version of Outlook and QBD. I begrudgingly switched to the old version but it still didn't work. I have tried all the fixes; check run as admin, check that outlook is checked in preferences, fix mapi, etc. Nothing works.
Exasperated, I switched my preference to webmail and I logged into my O365 account for work and believe it or not, it worked! You have to jump through a few authentication hoops but I can now send emails using my work/O365 account! Hope this helps someone.
And... I've switched back to new Outlook.
