Admins may be unable to complete mailbox migrations in Exchange Online

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may have been unable to complete mailbox migrations in Exchange Online. More info: This issue only affected multi-geo tenants. Final status: The remaining mailboxes have been moved to their default portion of infrastructure and we've confirmed that the impact is remediated. Scope of impact: Multi-geo admins may have been unable to complete mailbox migrations in Exchange Online. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC End time: Sunday, March 8, 2026, at 7:00 PM UTC Root cause: A recent service change, intended to optimize how requests were routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, caused migration batches to fail because the migration mailbox was in a different location than the user mailbox, and caused impact. Next steps: - We're reviewing our service change testing and validation procedures to identify and prevent similar mailbox location mismatches in changes moving forward. This is the final update for the event.

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: We've resumed and are monitoring the remaining mailbox moves in the final impacted region. Our migration timeline estimates that all mailboxes will have been relocated and that impact will be remediated by our next scheduled communication update. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Monday, March 9, 2026, at 7:00 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: The mailbox moves have completed in all regions except Canada, which have stalled. We're investigating why the Canada-based mailboxes moves have stalled so that we can complete them as quickly as possible and fully remediate impact. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Wednesday, March 4, 2026, at 8:00 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: The mailbox moves are continuing to progress, and many users have begun seeing relief of impact. However, additional time is needed for this process to fully complete and mitigate this event for all affected users. We anticipate that the mailbox moves will be completed for all users by our next scheduled update. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Monday, March 2, 2026, at 8:00 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: Our work on the mailbox moves continues and many have already completed. However, additional time is needed to finish moving the mailboxes. We'll provide a timeline for the completion of the process as soon as one is available. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Friday, February 27, 2026, at 8:00 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: Our efforts to move the migration mailboxes back to their default portion of infrastructure is still ongoing. We'll provide a timeline for the completion of this action as one becomes available. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Thursday, February 26, 2026, at 7:30 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: We've updated our "Root cause" section to provide further detail. We've confirmed that our fix designed to exempt the affected migration mailboxes from the load balancing actions that move the mailboxes between portions of infrastructure has completed deployment. We're now moving the migration mailboxes back to their default portion of infrastructure, so that admins can successfully complete their mailbox migrations. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Tuesday, February 24, 2026, at 7:30 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: We’ve identified that the fix has reached 90 percent saturation and expect the deployment to complete by our next scheduled update. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Friday, February 20, 2026, at 7:30 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: We've identified a list of mailboxes that have been impacted by this issue and have manually applied mitigations to restore them. The long-term fix to prevent this issue from impacting new mailbox migrations is still deploying and we expect that it will complete deployment by the time of our next update. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Tuesday, February 17, 2026, at 7:00 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: We've begun deploying our tool to prevent the issue from affecting further mailbox migrations, and anticipate this deployment will complete by our next scheduled communication update. While the deployment is ongoing, we're running a script to identify previously affected migration and system mailboxes so that we can manually apply our mitigation to them. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Start time: Wednesday, January 7, 2026, at 9:43 PM UTC Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Tuesday, February 10, 2026, at 7:00 PM UTC

Title: Admins may be unable to complete mailbox migrations in Exchange Online User impact: Admins may be unable to complete mailbox migrations in Exchange Online. More info: This issue only affects multi-geo tenants. Current status: We've identified an issue that's affecting the ability to complete mailbox migrations in Exchange Online, which is the result of a recent service configuration change that was intended to optimize how requests are routed within the service. We've applied a configuration change to the migration mailbox and system mailbox locations to remediate the issue, which succeeded for a subset of admins. However, some admins are still unable to complete mailbox migrations. We're developing a tool to proactively identify migration mailboxes and system mailboxes experiencing the issue and correct their locations to remediate impact. We anticipate this tool may be ready for deployment by our next scheduled communication update. While we work to complete development of the tool, any admins experiencing the issue can escalate through their support resources to request a manual mitigation. Scope of impact: Multi-geo admins may be unable to complete mailbox migrations in Exchange Online. This information may be updated as our investigation continues. Root cause: A recent service change, intended to optimize how requests are routed within the service by moving migration mailboxes to alternate portions of infrastructure as a load balancing effort, causes migration batches to fail because the migration mailbox is in a different location than the user mailbox, causing impact. Next update by: Friday, February 6, 2026, at 7:00 PM UTC