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

10/01/2025 07:40:00 AM

NHSmail Reference: INC47951149

Microsoft Reference: EX975862

Issue Status: RESOLVED

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

Final Update: 28/01/2025 17:40:00 AM Following the deployment of Microsoft’s fix and the successful rollback of the offending service update, their internal telemetry has confirmed that impact has been remediated.

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 steps: Microsoft are further analyzing both the offending migration and the affected subset of Outlook calendar infrastructure so they can help prevent similar problems with future planned migrations.

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