Assigned throttling policy has been configured for Exchange 2010. Why does the default throttling policy supersede the throttling policy assigned to the Migration Manager service account?
When Exchange 2010 evaluates which throttling policy to enforce, it will look for the throttling policy with the higher value.
The default throttling policy contains the following values:
RCAMaxConcurrency - 20
RCAPercentTimeInAD - 5
RCAPercentTimeInCAS - 205
RCAPercentTimeInMailboxRPC - 200
Setting RCAMaxConcurrency, RCAPercentTimeInAD, RCAPercentTimeInCAS, RCAPercentTimeInMailboxRPC to $null in an assigned policy will result in Exchange enforcing the Default Throttling Policy as it has the higher value for these parameters.
To prevent the Default Throttling policy from superceding the assigned policy, set the values for RCAMaxConcurrency, RCAPercentTimeInAD, RCAPercentTimeInCAS, RCAPercentTimeInMailboxRPC in the assigned throttling to a higher value; such as 9000.