Microsoft warns administrators against moving mailboxes within tenants

"Microsoft explains that this functionality does exist for historical reasons, but is not officially supported by the company. There are several reasons for this. First, Microsoft cannot easily troubleshoot or expedite local moves. Once these requests are initiated, they are given low-priority background task status, which can sometimes take weeks. In addition, Exchange Online has automated processes, eliminating the need for manual local moves, which are also inefficient."

"There is also a risk of so-called orphaned data. Move requests can be used for Primary Mailboxes and MainArchive Mailboxes. Local move requests are in principle possible for moving these components within the data center environment, but great caution is required. When the user is updated at the end of the local move, the update code only knows the properties that refer to the Primary and MainArchive."

Microsoft warns administrators that using the New-MoveRequest cmdlet for local mailbox moves in Exchange Online is unsupported and can cause operational problems. Local move requests receive low-priority background task status and can take weeks to complete, limiting Microsoft’s ability to troubleshoot or expedite them. Exchange Online uses automated placement and load balancing that makes manual local moves unnecessary and inefficient. Local moves risk orphaned data: the completion update only knows Primary and MainArchive properties, and moves against MailboxLocation-based shards can reset the Primary shard’s Database property, creating a dialtone mailbox. The cmdlet remains available for other move scenarios.

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