Microsoft 365 Alert – Service Degradation – Microsoft Teams – Admins may be unable to progress mailbox migrations in Exchange Online – RESOLVED

17/04/2026 9:20:00 AM

NHSmail Reference: INC46801881

Microsoft Reference: EX1280763

Issue Status: RESOLVED

Issue Description: Admins may be unable to progress mailbox migrations in Exchange Online.

More info: All mailbox migrations from on-premises to Exchange Online and tenant-to-tenant remain in a syncing state.

Final Update: 28/04/2026 8:44:00 AM– Microsoft has confirmed that our deployment of a code fix to address an offending service-side update has completed and impact is remediated.

Scope of impact: All admins attempting mailbox migrations from on-premises to Exchange Online are impacted. This information may be updated as our investigation continues.

Root cause: A recent service-side update introduced an issue that is causing migration jobs to fail, resulting in impact.

Next update by: Microsoft are analyzing the offending service-side update to determine why the potential for impact wasn’t caught during our internal update testing and validation phases. This analysis will help us to improve our update testing processes moving forward to ensure similar impact scenarios don’t occur in the future.