Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may be unable to send or receive email from the Outlook mobile app on their devices – RESOLVED

22/08/2025 08:50:00 AM

NHSmail Reference: INC46610640

Microsoft Reference: EX1137017

Issue Status: RESOLVED

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).

Final Update: 15/09/2025 08:53:00 AM – Microsoft have completed deployment of the fix across all affected environments, and after monitoring the service, they have verified that the issue has been successfully resolved.

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 Steps: Microsoft are investigating how the recent build update introduced a condition that, when a transient failure occurred, generated an exception for a subset of users and caused the sync job responsible for outbound and inbound mail to be placed in a quarantine state to prevent recurrence.