1.) Run the following cmdlets in an Exchange Management Shell:
New-ThrottlingPolicy MigPolicy
Set-ThrottlingPolicy MigPolicy -RCAMaxConcurrency Unlimited -EWSMaxConcurrency Unlimited -EWSMaxSubscriptions Unlimited -CPAMaxConcurrency Unlimited -EwsCutoffBalance Unlimited -EwsMaxBurst Unlimited -EwsRechargeRate Unlimited
Set-Mailbox <MigAdminUser> -ThrottlingPolicy MigPolicy
Where 'MigAdminUser' is the name of your migration admin account.
2.) For the throttling policy to take effect immediately, restart the Exchange RPC Client Access service.
Note: If the Exchange RPC Client Access service is not restarted, it might take the throttling policy up to two hours or longer to take effect.
