Source mailbox already being moved errors while moving mailboxes

It’s been a long time since I wrote a blog post, but this one comes up a lot so I figured I’d do a write-up on it. When moving mailboxes using to Exchange 2010, Exchange 2013, Exchange 2016, or Exchange Online (Office 365), a common error you can hit is SourceMailboxAlreadyBeingMovedTransientException.  What this appears to…

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