Building a custom recipient scope that applies to specific users in a certain OU in Active Directory by using a RecipientRoot parameter. To create exchange 2010 custom recipients scope do the follow:
New-ManagementScope “New-Management-Scope-Name” –RecipientRoot “OU=OU_Name,DC=DomainName,DC=com” It’s also possible to use RecipientRestrictionFilter, for example to add it the recipient scopes of all users with mailboxes so concatenating to the string above along with this string:
-RecipientRestrictionFilter  {RecipientType -eq “UserMailbox”}