Microsoft released a guided walkthrough troubleshooter (GWT) that is designed to assist when having issues moving a mailbox from an on-premises Exchange environment to Exchange Online (On-Boarding). This will also assist when moving a mailbox back on-premises from Exchange Online (Off-boarding).
The intent of this GWT is to take a tenant administrator step-by-step though the common troubleshooting tasks to solve their hybrid mailbox move issues and allow the customer to continue their deployment. Microsoft took the most common migration failure scenarios and put them into this easy to follow guide.
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