Which permissions must I give my Help desk staff to enable them to create mailboxes?
To enable Help desk staff or other nonadministrators to create mailboxes on existing accounts, you need to use the Windows 2000 Delegation of Control Wizard to give the Help desk group the necessary Active Directory (AD) permissions. The Help desk group will also need at least Exchange View Only Administrator permissions for the administrative groups that host the stores in which the Help desk staff will create mailboxes. By controlling which administrative groups the Help desk group has permissions for, you can control on which accounts the Help desk staff can create mailboxes.
—Paul Robichaux