Mailbox Migration from O365 to On-Prem Error: EvaluationException:

Hi Clark_Avatara,

The "EvaluationException" error is a general issue that can stem from various factors.
When dealing with mailbox migration from Office 365 to on-premises, it commonly arises due to one of the following:

1. Issues related to the mailbox hierarchy, which may result from mailbox corruption or synchronization problems between Office 365 and on-premises systems.

2. Problems within the migration batch, which could result from improper batch configuration or issues occurring during the migration process.

3. Complications arising from the on-premises Exchange server, which might be due to hardware failures, software glitches, or configuration errors.

Given that you're encountering this error on 14 different mailboxes, it's less likely to be related to the individual mailboxes themselves and more likely tied to problems within the migration batch or the on-premises Exchange server.

1. Verify the configuration of the migration batch. Make sure that the batch is configured correctly and that all of the required parameters are set.
2. Check the health of the on-premises Exchange server. Make sure that the server is running properly and that there are no hardware or software problems.
3. Run the Microsoft Exchange Hybrid Configuration Wizard. This wizard can help to troubleshoot problems with hybrid deployments and can sometimes resolve the EvaluationException error.

If you have tried all of the above and are still unable to resolve the error, you may need to migrate the mailboxes manually.

Here are some links that can be useful:

• Unable to move a mailbox from Microsoft 365 back to on-premises in hybrid: https://learn.microsoft.com/en-us/exchange/troubleshoot/move-mailboxes/hybrid-move-fails
• Move mailboxes between on-premises and Exchange Online: https://learn.microsoft.com/en-us/exchange/hybrid-deployment/move-mailboxes