“The Exchange Messaging team was successfully able to get Hybrid Modern Authention (HMA) functioning with 0365 and on Premise Exchange 2016. Outlook clients are currently working as expected, however, we have seen the default email address being used for the default username during the initial login prompt from 0365. This is a known issue when the primary SMTP address and the User Principal Name (UPN) do not match. During this prompt all users must select “Use Different Account” and use their UserName@umsystem.edu
to login. If that does not work, please reboot the workstation and try again.
Additionally, OWA is currently not working as expected due to a technical issue with setting up the service with 0365. The Messaging team is has a case open with Microsoft 0365 services. We will provide updates as we continue to investigate.”