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When you run the Export-Mailbox command on a Microsoft Exchange 2007 mailbox that has more than 5000 items in one folder, the command fails. Additionally, you receive the following error message:
Export-Mailbox: Error was found for <mailbox name> (<SMTP address>) because: Error occurred in the step: Moving messages. Failed to copy messages to the destination mailbox store with error: An unknown error has occurred. error code: -1056749164
For example, this problem occurs when you run the following command in the Exchange Management Shell: