Microsoft 365 Alert – Service Degradation – Exchange Online – Some users can’t create or access public folders through the Outlook desktop client and Outlook on the web – RESOLVED

Announcements Sourav Nandi

19/08/2025 11:10:00 AM

NHSmail Reference: INC46607607

Microsoft Reference: EX1137566

Issue Status: RESOLVED

Issue Description: Some users can’t create or access public folders through the Outlook desktop client and Outlook on the web.

More info: Some users are also reporting failures when attempting to delete public folder subfolders, and are experiencing public folder permission delays.

Final Update: 21/08/2025 08:55:00 AM – Microsoft have reverted the offending change and confirmed after monitoring service telemetry, that impact has been remediated.

Scope of impact: Impact is specific to some users who are served through the affected infrastructure, attempting to utilize public folders through the Outlook desktop client and Outlook on the web.

Root cause: A recent deployment intended to optimize the Messaging Application Programming Interface (MAPI) storage systems introduced an issue that caused failures to occur in the impacted scenario, which led to impact.

Next steps: Microsoft are reviewing their deployment procedures to better identify similar issues during our development and testing cycles.