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

25/03/2026 8:23:00 AM

NHSmail Reference: INC46781709

Microsoft Reference: EX1259460

Issue Status: ONGOING

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

Current Update: 25/03/2026 8:59:00 AM – Microsoft has identified that a recent service update is affecting Exchange Web Services which impacts add-ins in Exchange Online. While they continue their investigation to confirm this theory, they recommend following the guidance in the “More Info” section to verify that Exchange Web Services access is enabled and then testing to validate whether the customer add-ins are accessible.

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 update by: Monday, March 30, 2026, at 9:00 PM UTC