1. No we have not received a service upgrade notification.
2. We have tried using other mail services such as thunderbird and outlook. Users logging in as themselves works fine, Adminsitrator logins as other users do not. (They used to work.)
I have tried changing the server to outlook.office365.com. This appeared to work, and occassionaly works maybe one out of every 50 tries.
Possible question... Is the administrator login now restricted to one login at any time?