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Fix Exchange Mailbox Migration Quota Errors for E3 Users
Question details
Users need to resolve a migration failure where mailboxes between 50 GB and 100 GB fail to migrate to Microsoft 365 due to an incorrect 50 GB quota limit.
- Product
- Microsoft Exchange Server
- Device & OS
- not provided
- Scenario
- Performing a hybrid Exchange mailbox migration for users who have been assigned Microsoft 365 E3 licenses.
- Observed behavior
- The migration process incorrectly reports a 50 GB quota limit and fails for mailboxes sized 50-100 GB, despite the E3 license supporting 100 GB capacities.
Verify that the target user accounts are successfully assigned valid Microsoft 365 E3 licenses and confirm the exact size of their current on-premises mailbox data before proceeding.
Enable In-Place Archive and Verify Exchange Quotas
Enabling an in-place archive allows you to split the mailbox data, circumventing the incorrect quota threshold during the migration sync.
In some hybrid setups, legacy configuration attributes might incorrectly enforce a standard 50 GB threshold on the migration batch. Moving older emails to an in-place archive helps bypass this by splitting the total storage.
Log into your on-premises Exchange Admin Center and verify the mailbox quota settings to ensure they are not artificially capped at 50 GB for the affected users.
In the Exchange Admin Center, locate the user mailbox, navigate to the mailbox features, and enable the In-Place Archive option.
Once the archive is generated and data is moved, initiate the migration for both the newly created archive and the primary mailbox to Microsoft 365.
Review Large-Item Limits and Clean Up Mailbox
Migrations can fail if the mailbox contains items that exceed the maximum size or quantity limits allowed by Exchange Online.
Submit a Microsoft 365 Support Request
If configuration adjustments do not resolve the incorrect 50 GB quota enforcement, backend support from Microsoft is required to analyze the logs.
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Frequently Asked Questions
Why does my E3 license migration say there is a 50GB limit?
In some hybrid Exchange deployments, legacy routing rules or on-premises configurations incorrectly apply the default 50 GB threshold of lower-tier licenses. Splitting the mailbox via an in-place archive usually bypasses this error.
What is the actual primary mailbox size limit for an M365 E3 user?
A Microsoft 365 E3 license includes a 100 GB primary mailbox capacity. Additional storage is available if you enable auto-expanding archiving.
Can I directly migrate an on-premises mailbox larger than 100GB to Microsoft 365?
No, you cannot migrate a primary mailbox larger than 100 GB directly. You must first enable archiving on-premises, move sufficient data to the archive to bring the primary mailbox under 100 GB, and then perform the migration.
Where can I find the migration error logs to send to Microsoft Support?
Migration logs can be found in the Exchange Admin Center under the Migration tab. Select your specific migration batch, click on 'View details' for the affected user, and download the diagnostic report.
