I was working with a customer last week that is interested in deploying the RBAC split permissions model rather than the default shared permissions model that is used in Exchange 2010. I just wanted to step through the configuration process in this article and also wanted to amplify an important point regarding permissions bypass found in the RBAC split permissions deployment instructions on TechNet.
Let's first take the scenario of a default installation that uses shared permissions. In my lab environment, my user account has been delegated the Exchange Organization management role. As a result of these permissions, I can elect to perform some Active Directory related tasks within the Exchange Management Shell or Exchange Management Console such as the deleting of Active Directory user accounts when deleting the corresponding mailbox. For example, in Figure 1 below you can see that I have the ability to perform the Remove command when right-clicking a mailbox in the Exchange Management Console; this in turn also removes the Active Directory account. The same result can be achieved by running the Remove-Mailbox cmdlet in the Exchange Management Shell.

Figure 1 - Removing Active Directory Objects
Having been delegated the Exchange Organization management role also means that my user account can create new Active Directory objects in addition to deleting them. How can this situation be addressed? How can we ensure that pure Exchange administrators cannot, say, delete Active Directory objects? Deploying RBAC split permissions is one of the options available to you to achieve this. Switching to RBAC split permissions largely involves running a series of Exchange Management Shell cmdlets, as it's not possible to configure RBAC split permissions via the Exchange Management Console. Let's walk through the process.
The first thing to do is to create a new role group for the Active Directory administrators. This role group should be assigned the roles required to allow its members to modify Active Directory objects, namely the Mail Recipient Creation and Security Group Creation and Membership roles. Optionally, the Role Management role can also be included at the same time if required, since this allows members of the new role group the ability to assign the Mail Recipient Creation and Security Group Creation and Membership roles to other role assignees in the future. I'll also talk a bit more about the Role Management role later in this article, as there is a permissions bypass issue that you may want to address.
The cmdlet to use to create the new role group is the New-RoleGroup cmdlet, which will create the new role group in the Microsoft Exchange Security Groups Organizational Unit (OU) along with the other default role groups. The -Roles parameter is used to specify the management roles to assign to this role group and I also like to include the -Description parameter as the default role groups also have their description fields populated with meaningful descriptions of what the role group does. The full command that I have run is:
New-RoleGroup "Active Directory Administrators" -Roles "Mail Recipient Creation", "Security Group Creation and Membership" -Description "Members of this management role group have permissions to manage Active Directory objects"
The result of running this command is the new role group as you can see from Figure 2.

Figure 2 - New Active Directory Administrators Role Group
The next step is to create delegating role assignments between the Active Directory Administrators role group and the roles assigned to this role group; the roles assigned were the Mail Recipient Creation and the Security Group Creation and Membership roles. These delegating role assignments give the role assignee, namely the Active Directory Administrators group members, the ability to assign the role to other role assignees if required. The following commands will achieve this objective:
New-ManagementRoleAssignment -Role "Mail Recipient Creation" -SecurityGroup "Active Directory Administrators" -Delegating
New-ManagementRoleAssignment -Role "Security Group Creation and Membership" -SecurityGroup "Active Directory Administrators" -Delegating
Now that we have our Active Directory Administrators role group created, I'm going to add my Active Directory account to it. Furthermore, another Active Directory account, named Sally, that has also been delegated the Exchange Organization management role will not be made a member of this new role group so that we can compare the permissions available to the two accounts. To add my account to the new role group, the command to run is simply:
Add-RoleGroupMember "Active Directory Administrators" -Member Neil
To ensure that only members of the Active Directory Administrators role group can modify membership of this same group, the ManagedBy parameter of the role group is set to the Active Directory Administrators group via the Set-RoleGroup cmdlet:
Set-RoleGroup "Active Directory Administrators" -ManagedBy "Active Directory Administrators"
This makes the change that you can see in Figure 3. By default, the ManagedBy attribute was set to the Exchange Organization management role group when it was first created.

Figure 3 - Setting The ManagedBy Attribute
Operationally, if a non-member of the Active Directory Administrators role group then tries to modify the membership of this group, the operation will fail with a permissions failure as you can see in Figure 4:

Figure 4 - Membership Change Permissions Failure
However, members of the Exchange Organization management role group can bypass the security check we configured as a result of the Set-RoleGroup command earlier in this article. Specifically, it's actually anyone who is assigned the Role Management role which is the case, by default, for anyone who is a member of the Exchange Organization management role. For example, the other Exchange administrator called Sally is a member of the Exchange Organization management role group but is not a member of the Active Directory Administrators role group that we have just created. In this scenario we do not want to give Sally the ability to manage Active Directory objects, such as deleting Active Directory accounts when deleting mailboxes. However, Sally can run the following command to grant herself membership of the Active Directory Administrators role group:
Add-RoleGroupMember "Active Directory Administrators" -Member Sally -BypassSecurityGroupManagerCheck
The -BypassSecurityGroupManagerCheck parameter allows Sally to add herself to the Active Directory Administrators role group even though we have previously configured the group such that only members of the group itself can manage the group membership. To prevent this from happening, we can remove the Role Management role group from the permissions assigned to our Exchange administrators. However, I'm not going to go that far in this article as I'm going to choose to monitor the membership of the Active Directory Administrators group.
To complete our RBAC split permissions configuration, we need to remove the management role assignments for the Mail Recipient Creation and Security Group Creation and Membership management roles. To do this, we can run the following commands:
Get-ManagementRoleAssignment -Role "Mail Recipient Creation" | fl name
Get-ManagementRoleAssignment -Role "Security Group Creation and Membership" | fl name
The results of running these commands are shown in Figure 5.

Figure 5 - Management Role Assignments
It's now just a case of removing the management role assignments not linked with the Active Directory Administrators role group using the following commands:
Remove-ManagementRoleAssignment "Mail Recipient Creation-Organization Management-Delegating"
Remove-ManagementRoleAssignment "Mail Recipient Creation-Organization Management"
Remove-ManagementRoleAssignment "Mail Recipient Creation-Recipient Management"
Remove-ManagementRoleAssignment "Security Group Creation and Membership-Organization Management-D"
Remove-ManagementRoleAssignment "Security Group Creation and Membership-Organization Management"
All that's left to do now is to logon as Sally and confirm the permissions that are available to this administrator. Remember, this administrator is not a member of the Active Directory Administrators role group and therefore should not be able to, for example, delete Active Directory objects when deleting the corresponding Exchange mailbox. As you can see from Figure 6, this is now confirmed as the Remove menu option is not available to this administrator:

Figure 6 - Remove Command Missing