Reports are showing up online that users may be unable to connect to the Exchange Online service.
Several users here at Cayosoft report not being able to connect to the full-Outlook client to Exchange Online, however the web based version of Outlook appears to be working.
Current status as of 11:55 AM 6/15/2020: We’re investigating an issue with the Outlook client within Europe. Please follow EX216336 in your dashboard for further information.