Microsoft 365 Alert – Service Degradation – Exchange Online – Users may be unable to complete mailbox offboarding because the migration task is blocked and can’t finish – RESOLVED

24/08/2026 09:30:00 AM

NHS.net Connect Reference: INC46916720

Microsoft Reference: EX1458145

Issue Status: RESOLVED

Issue Description: Users may be unable to complete mailbox offboarding because the migration task is blocked and can’t finish.

Final Update: 28/08/2026 08:52:00 AM – Microsoft has completed deployment of their fix faster than initially anticipated and validated after a period of monitoring service availability that their actions successfully remediated impact.

Scope of impact: Users attempting to complete mailbox offboarding in Exchange Online may have been impacted by this issue.

Root cause: The mailbox migration task was being delayed due to the integrity validation process remaining pending at the completion stage, resulting in impact.

Next steps: Microsoft is analysing the offending integrity validation process to validate how it was introduced into their service and to confirm what actions they can take to prevent similar impact scenarios from occurring in the future.