Over the past week we have received a number of tickets where Microsoft Outlook requests users enter their credentials over and over. In an effort to provide a resolution our research discovered this is a known issue and Microsoft is working on a resolution. Below is the information we have received from Microsoft and the recommended work-around during this service interruption.
From Microsoft: Office 365 is experiencing an issue with Outlook users receiving repeated credential prompts within the Outlook client and getting disconnected. The issue stems from a recent update to Microsoft’s Exchange servers that contained a code issue which causes Outlook to keep prompting the user for credentials. The issue was first reported and confirmed to affect a subset of Office 365 users on May 5, 2020 by Microsoft and Microsoft has yet to release an update announcing a fix to the problem.
If you are experiencing this issue, Microsoft recommends users to use alternative means of accessing their email, either through mobile devices or through the OWA which is accessible at outlook.office365.com to manage their mailbox until Microsoft remediates the issue.