Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may be unable to access custom add-ins through any Exchange Online connection method – RESOLVED

25/03/2026 8:23:00 AM

NHSmail Reference: INC46781709

Microsoft Reference: EX1259460

Issue Status: RESOLVED

Issue Description: Some users may be unable to access custom add-ins through any Exchange Online connection method.

Fina]l Update: 01/04/2026 8:50:00 AM– Microsoft are continuing to validate our suspected root cause as mentioned in our previous communication update, and they recommend following the guidance in the “More Info” section to verify that Exchange Web Services access is enabled. Once enabled, they request that impacted users validate whether the custom add-ins are accessible. If impact persists for users after enabling this, please contact them through their support case for further investigation.

Scope of impact: Some users who are attempting to access custom add-ins through all Exchange Online connection methods may be impacted. This section may be updated as our investigation continues.

Next Steps: Microsoft are reviewing how the impacting changes prevented users from accessing custom add-ins so we can avoid similar issues in the future, as EWS is slated to be deprecated by October 2026.