You need to meet the technical requirements for User1.

The requirement is narrow: User1 must be able to manage the membership of all the groups located in Contoso\OU3, and nothing more. The Delegation of Control Wizard, run against OU3 specifically, lets an administrator grant User1 exactly the built-in task " Modify the membership of a group, " which grants write access to the member attribute on group objects contained in that OU only. This satisfies the requirement while granting no rights outside OU3, which is the definition of least privilege. Creating the same delegation at the domain root (contoso.com) would technically work but grants far broader scope than needed, since it would apply to every container in the domain, not just OU3, violating least privilege. Adding User1 to Account Operators grants domain-wide rights to create, delete, and modify most user, group, and computer accounts throughout the domain (with some protections for built-in admin accounts), which is excessive for a task limited to group membership in one OU. Server Operators is unrelated to Active Directory object management altogether; it governs local administrative rights on domain controllers themselves. Therefore, delegating control on OU3 is the correct, minimally scoped solution.