Microsoft is introducing a new parameter that can be called by using the Set-User cmdlet in Exchange Online PowerShell. The new parameter is called "PermanentlyClearPreviousMailboxInfo". The feature is focused for customers doing migration of on-premises mailboxes to the cloud and you will be able to use it within few days. This will help us after we assigned license and due to GUID sync issue, we had two mailboxes in EXO and onprem server.
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