This problem occurs because the on-premises mailbox type is not correctly changed from “UserMailbox” to “RemoteMailbox.” Therefore, the mailbox cannot correctly route mail to Exchange Online.
- Restore the Exchange Online mailbox to your on-premises Exchange organization. To do this, go to the following Microsoft TechNet website, and then follow the steps in the “Move Exchange Online mailboxes to the on-premises organization” section in major step 3 ("Use the EAC to move mailboxes"):
- Force a full directory synchronization. To do this, follow the steps in the "Force directory synchronization" section of the following MSDN website:
- Restore the affected user mailbox to Exchange Online. To do this, go to the TechNet website from step 1, and then follow the steps in the “Move on-premises mailboxes to Exchange Online” section of major step 3.
Article ID: 2973898 - Last Review: 20 Dec 2016 - Revision: 1