Using classic Outlook for Windows in business environments
This might be of use to some users. I was having the same trouble with one of our accounts, and couldn't resolve it following any of the troubleshooting steps that had been provided. These are the steps I took:
- Force a sign out of all sessions in the Microsoft 365 admin center for the impacted user account
- Remove the account from Outlook
- Close Outlook
- Open Outlook and add the account again
I believe it would probably also work without removing the account, and by simply re-entering login credentials, but we're a few hours in, and the account is now working perfectly again. Hope this helps!