Rules failed to migrate.
Some mailbox rules may not migrate in Exchange to Exchange or Exchange to Office 365 migrations. This typically is due to the corresponding folders not being created at the Destination mailbox. For example, you may have a rule that all email from "email@example.com" are moved into the "User" folder. If the "User" folder isn't created at the Destination, that might be because the folder was deleted at the Source and the user simply didn't update the rule. Other rule migrations failures can occur if the rule is a client-only one.
The error will not result in a failed migration. The rules that failed will be added to the error list.
- Check the Exchange mailbox rules. Are the rules that failed marked as "client-only?" If so, they won't be migrated appropriately.
- If a failed rule requires the email to be moved to a specific folder, check to see that the folder still exists at the Source. If not, create the folder at the Source and perform a Delta migration.
- If the above steps don't work, contact support.
From the Microsoft Knowledge Base:
"Rules either run on the server or the client. Rules that run on the server are in effect even when you are not running Outlook (the client). Rules marked in the Rules Wizard as "(client-only)" may only work when you are running Outlook. If a rule requires access to your personal folders, it is a client-only rule, since your personal folders (.pst) file is located on your client computer. Rules that present you with a message are also client-side rules. If the rule only depends on mailbox folders, located on the server, then it is a server-side rule and can run as long as the mail server is running."