Admins may be unable to progress mailbox migrations in Exchange Online

Title: Admins may be unable to progress mailbox migrations in Exchange Online User impact: Admins may have been unable to progress mailbox migrations in Exchange Online. More info: All mailbox onboarding and offboarding scenarios in Exchange Online, including Tenant to Tenant migrations remained in a syncing state. Final status: We've 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 into or out of Exchange Online may have been impacted. Start time: Tuesday, April 14, 2026, at 11:20 AM UTC End time: Monday, April 27, 2026, at 4:39 PM UTC Root cause: A recent service side update introduced an issue that was causing migration jobs to fail, resulting in impact. Next steps: We're 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. This is the final update for the event.

Title: Admins are unable to progress mailbox migrations in Exchange Online User impact: Admins are unable to progress mailbox migrations in Exchange Online. More info: All mailbox onboarding and offboarding scenarios in Exchange Online, including Tenant to Tenant migrations remain in a syncing state. Current status: We’re continuing to monitor the fix as it propagates throughout the affected infrastructure, where deployment has now reached 90 percent. We’ll provide a resolution timeline once available. Scope of impact: All admins attempting mailbox migrations into or out of Exchange Online are impacted. Root cause: A recent service side update introduced an issue that's causing migration jobs to fail, resulting in impact. Next update by: Monday, April 27, 2026, at 6:30 PM UTC

Title: Admins are unable to progress mailbox migrations in Exchange Online User impact: Admins are unable to progress mailbox migrations in Exchange Online. More info: All mailbox onboarding and offboarding scenarios in Exchange Online, including Tenant to Tenant migrations remain in a syncing state. Current status: The fix has reached around 85 percent of the affected infrastructure and we're continuing to monitor as the fix deployment progresses and we expect it to complete by the next scheduled update. Scope of impact: All admins attempting mailbox migrations into or out of Exchange Online are impacted. Root cause: A recent service side update introduced an issue that's causing migration jobs to fail, resulting in impact. Next update by: Thursday, April 23, 2026, at 7:30 PM UTC

Title: Admins are unable to progress mailbox migrations in Exchange Online User impact: Admins are unable to progress mailbox migrations in Exchange Online. More info: All mailbox onboarding and offboarding scenarios in Exchange Online, including Tenant to Tenant migrations remain in a syncing state. Current status: We confirmed through internal testing in our internal environments the effectiveness of the fix and have begun broad deployment. The deployment is currently at 29% and progressing. We'll continue to monitor the deployment of the fix and provide additional status at next communication time. Scope of impact: All admins attempting mailbox migrations into or out of 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: Wednesday, April 22, 2026, at 7:00 PM UTC

Title: Admins may be unable to progress mailbox migrations in Exchange Online User impact: Admins may be unable to progress mailbox migrations in Exchange Online. More info: All mailbox onboarding and offboarding scenarios in Exchange Online, including Tenant to Tenant migrations remain in a syncing state. Current status: We've begun deploying our fix to revert the offending service update to our internal test environment to validate whether it resolves the issue prior to broad deployment. We anticipate our validations will complete, and broad deployment initiated by our next scheduled communications update. We'll continue reviewing potential short-term mitigation options, but our testing thus far hasn't revealed any viable actions besides the reversion. Scope of impact: All admins attempting mailbox migrations into or out of 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: Monday, April 20, 2026, at 6:00 PM UTC

Title: Admins may be unable to progress mailbox migrations in Exchange Online User impact: Admins may be unable to progress mailbox migrations in Exchange Online. More info: All mailbox migrations from on-premises to Exchange Online remain in a syncing state. Current status: We've begun deploying our fix to revert the offending service update to our internal test environment to validate whether it resolves the issue prior to broad deployment. We anticipate our validations will complete, and broad deployment initiated by our next scheduled communications update. We'll continue reviewing potential short-term mitigation options, but our testing thus far hasn't revealed any viable actions besides the reversion. 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: Monday, April 20, 2026, at 6:00 PM UTC

Title: Admins may be unable to progress mailbox migrations in Exchange Online User impact: Admins may be unable to progress mailbox migrations in Exchange Online. More info: All mailbox migrations from on-premises to Exchange Online remain in a syncing state. Current status: We’ve determined that a recent service-side update inadvertently introduced a dependency issue that is causing migration jobs to fail. We’re reverting the update that introduced the issue to remediate impact. We’re also exploring short-term mitigations to allow migrations to complete while the permanent fix is finalized and deployed. 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 inadvertently introduced an issue that is causing migration jobs to fail, resulting in impact. Next update by: Wednesday, April 15, 2026, at 6:00 PM UTC

Title: Admins may be unable to progress mailbox migrations in Exchange Online User impact: Admins may be unable to progress mailbox migrations in Exchange Online. More info: All mailbox migrations from on-premises to Exchange Online remain in a syncing state. Current status: We’re analyzing migration and move request diagnostics to understand why mailbox migrations aren’t progressing and to determine a remediation path. 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. Next update by: Wednesday, April 15, 2026, at 10:30 AM UTC