[German]Microsoft is investigating an issue with Exchange Online that causes emails to not sync with Outlook for 12 hours. This affects users of mobile devices where the Outlook client uses Hybrid Modern Authentication (HMA). Email access issues may then occur in Outlook.
The issue has been confirmed by Microsoft under EX1137017 in the Microsoft 365 Admin Center, as Bleeping Computer reports here.
Service Degradation – Exchange Online – Some users may be unable to send or receive email from the Outlook mobile app on their devices – ONGOING
Microsoft Reference: EX1137017
Issue Status: ONGOING
Issue Description: Some users may be unable to send or receive email from the Outlook mobile app on their devices.
More info: Affected users would be utilizing Hybrid Modern Authentication (HMA).
Current Update: 22/08/2025 08:50:00 AM – Microsoft are continuing to monitor the progress of the deployment as it continues to saturate the affected environment. They'll provide a timeline for the completion of the deployment as one becomes available.
Scope of impact: Some users attempting to send or receive email from the Outlook mobile app may be impacted.
Root cause: A recent build update introduced a condition where, upon encountering a typical transient failure, an exception is generated for a subset of users that results in the sync job responsible for syncing outbound and inbound mail being placed in a quarantine state, resulting in syncs being delayed for a 12-hour interval.
Next update by: Monday, August 25, 2025, at 9:00 PM UTC
HMA is a feature of Microsoft Exchange Server that allows users to access local mailboxes from the cloud using authorization tokens. The above issue was caused by a recent service change designed to improve mailbox synchronization efficiency, but which is causing 12-hour synchronization delays for affected customers. Microsoft is working to resolve an issue with Exchange Online.
