Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may be unable to access or load Outlook on the web – RESOLVED

Announcements Shagufta Naaz

23/01/2026 11:23:00 AM

NHSmail Reference: INC46731927

Microsoft Reference: EX1221742

Issue Status: RESOLVED

Issue Description: Users may be unable to access or load Outlook on the web.

Final Update: 26/01/2026 08:38:00 AM – After monitoring the service recovery progress, Microsoft has confirmed that the service availability has reached expected levels and impact is remediated.

Scope of impact: This issue may impact any user within your organisation served via the affected region(s): United States, France and United Kingdom. This information may be updated as our investigation continues.

Root cause: A recent code regression was causing crashes on a portion of mailbox infrastructure that handles access requests from Outlook on the web, New Outlook, Outlook for Mac, and mobile apps.

Next Steps: Microsoft are investigating further into the recent code regression to better understand why it caused the inability to access Exchange Online and why impact was caught sooner so that they can proactively identify similar issues in the future.