From Microsoft: - problem resolved at 2:45pm (5/13)
All users may be unable to access the Exchange Online service (webmail) User Impact: Users may be unable to sign in to the Exchange Online service. More info: Users may encounter an error with the following message: "AADSTS50011: The reply URL specified in the request does not match the reply URLs configured for the application: 'e48d4214-364e-4731-b2b6-47dabf529218'".
Current status: Additional investigation determined that a recent change contained a code regression that resulted in authentication failures within Outlook on the web. We've disabled deployment and are currently in the process of rolling the affected change back to mitigate impact. Scope of impact: This issue may potentially affect any user. Root cause: A recent change included a code regression that resulted in users experiencing authentication failures. Next update by: Wednesday, May 13, 2020, 3:00 PM (8:00 PM UTC