Fix Exchange Hybrid Migration Mailbox Locked at 95 Percent
Question details
Users need to resolve a situation where specific mailboxes fail to complete migration, getting stuck right before finishing.
- Product
- Microsoft Exchange
- Device & OS
- not provided
- Scenario
- Performing a final incremental synchronization during an Exchange hybrid migration.
- Observed behavior
- The migration batch remains stuck at approximately 95 percent for affected mailboxes because they become locked, while other mailboxes complete successfully.
Ensure you have global administrator access to the Exchange Admin Center (EAC) and have the necessary permissions to view migration batch logs.
Review Migration Logs and Escalate to Support
Because mailbox locks at 95% during hybrid migrations can be triggered by complex underlying issues, the most reliable approach is to extract the diagnostic logs and consult Exchange specialists.
At 95% completion, Exchange is attempting the final synchronization and switchover. Locks occurring at this stage often involve corrupted items, target mailbox quota issues, or Active Directory replication delays that require backend diagnostics.
Log into the Exchange Admin Center (EAC) for your Exchange Online environment using your administrator credentials.
In the left-hand navigation menu, click on 'Recipients' and then select the 'Migration' tab to view all active batches.
Highlight the migration batch that contains the locked mailbox stuck at 95 percent.
Click on 'View details' in the right pane. Select the specific mailbox that failed, and click the option to download the synchronization and move-request error logs.
Open a support request through the Microsoft 365 Admin Center under 'Support' > 'Help & support', and attach the downloaded error logs for the Exchange hybrid specialists to investigate.
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Frequently Asked Questions
Why does an Exchange migration specifically get stuck at 95 percent?
The 95 percent mark in an Exchange hybrid migration represents the final incremental synchronization where the system locks the source mailbox to perform the final data switchover. Issues like corrupted items, conflicting AD attributes, or backend connectivity drops often cause it to hang precisely at this stage.
Can I increase the bad item limit to bypass the 95 percent lock?
In some cases, increasing the 'BadItemLimit' or 'LargeItemLimit' via PowerShell can allow a stuck migration to proceed. However, you should only do this after reviewing the move-request logs to confirm that skipping those specific corrupted items won't result in the loss of critical data.
Where can I find the specific error causing the lock?
You can locate the detailed errors in the Exchange Admin Center under 'Recipients' > 'Migration'. Select your batch, click 'View details' under Mailbox status, choose the affected user, and review the 'Data consistency score' or download the diagnostic report.
