Error
ErrorServerBusy
Cause
Exchange Web Services reported that a mailbox cannot be accessed because of throttling limits imposed by Exchange.
Resolution
Check the error to determine if it was reported for the source or destination system.
- If migrating from or to Office 365, enable impersonation to reduce the effect of throttling.
- If migrating from or to Exchange 2010 or later, and you have control over the email system, disable the Exchange throttling policy.