Microsoft 365 Alert – Service Degradation – Exchange Online – Users may be unable to share their Outlook calendars externally across any Exchange Online connection method – ONGOING

10/01/2025 07:40:00 AM

NHSmail Reference: INC47951149

Microsoft Reference: EX975862

Issue Status: ONGOING

Issue Description: Users may be unable to share their Outlook calendars externally across any Exchange Online connection method.

Current Update: 17/01/2025 09:02:00 AM – The rollback continues to progress throughout the affected environment. Microsoft are continuing to monitor the rollback to ensure it has the desired effect of remediating impact.

Scope of impact: Impact may occur for any user attempting to externally share their Outlook calendars across any Exchange Online connection method.

Root cause: A recent migration for a service that supports external calendar sharing is causing a section of Outlook calendar infrastructure to operate below acceptable performance thresholds.

Next Update by: Friday, January 17, 2025, at 8:00 PM UTC