Can an OU remove the group Domain Admins from having admin rights?
Every object in the Active Directory forest, including OU’s, can have explicit allow or deny permissions. The purpose of the Domain Admin account is NOT to administer the OUs but the Domain Admins permissions in order to administrate the domain, which includes setting up the department OUs. Once this is setup and delegated to the OU accounts, the permissions can be removed. If this is the situation, and there is a case where the domain admin have to make changes for the OU administrator, ownership must be assumed of the OU, and reset the permissions in order to make the changes.
