A Role Based Access Control (RBAC) role assignee who you want to restrict from running *-Message cmdlets, such as the Export-Message cmdlet, cannot be restricted from running these cmdlets by using a custom write scope.
To resolve this issue, install the following update rollup:
2936871 Update Rollup 6 for Exchange Server 2010 Service Pack 3
Microsoft has implemented this feature in Update Rollup 6 for Exchange Server 2010 Service Pack 3.
For more information about RBAC, go to the following Microsoft website: