Mail app no longer accepts my Exchange password (macOS Mojave)

Two days ago Mac Mail (Version 12.4 on Mojave 10.14.6) no longer accepted my Exchange password. I've tried everything I can think of: - Changed password in Office 365 Admin Center. - Exchange account still works fine on my iPhone, as well as in Web Mail. - Removed Mail Account and deleted account under Internet Accounts. - When I try to recreate Internet Account, it recognizes my user name, but when I enter the password it gets stuck on a grey window with a spinning gear. - Back in mail, the Account is there, but again it tells me the password is bad. I've retried these steps many, many times. - Safe Boot does not help. - The mail account works fine in Outlook for Mac (but I prefer to use Mail which we use business-wide). - I created a test user account to see if it's a User library issue. In the test account, the same problem occurs. - I have a 2nd Exchange account which continues to work fine. I was able to recreate that 2nd Exchange account in my test User account as well. Because the problem persists in a new test Mac account, I don't believe it's a Mac user account issue. Because the Exchange account works fine on my iPhone, as well as in Outlook, I don't think it's an Exchange account issue. And because I have a 2nd Exchange account working fine in Mail, I don't think it's a Mail/Exchange issue. If anyone has any suggestions I would be incredibly grateful!