Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may have the new Outlook client open in their web browser instead of the Desktop client – RESOLVED

Announcements Sourav Nandi

20/10/2025 08:40:00 AM

NHSmail Reference: INC46658945

Microsoft Reference: EX1173600

Issue Status: RESOLVED

Issue Description: Some users have the new Outlook client open in their web browser instead of the Desktop client.

More info: As a workaround, users are able to use the classic Outlook to access their Exchange Online mailbox.

Final Update: 21/10/2025 08:30:00 AM – Microsoft’s fix deployment is complete, and they’ve confirmed from service telemetry that this issue is resolved. Affected users may need to restart Outlook, potentially more than one time, to pick up the fix.

Scope of impact: Your organization is affected by this event, and some users attempting to open the new Outlook client are impacted.

Root cause: A code issue contained in a recent service update is causing a race condition and resulting in the impact.

Next steps: Microsoft are continuing their investigation to determine exactly how the offending code bug was introduced to better detect and prevent issues like this from occurring in the future.