Creating Recipients
After Exchange has extended Active Directory Users and Computers, you can mail-enable or mailbox-enable an object, and thereby turn the Active Directory object into a recipient. However, not all objects can be mail-enabled or mailbox-enabled. For example, you can create a mailbox for a user object or a mail-enabled group object, but you cannot do either for a computer object. Therefore, the Active Directory objects that are of most interest to you as an Exchange administrator are:
Users
InetOrgPerson objects
Contacts
Groups
Query-based distribution groups
For more information about creating recipients, see "Managing Recipients and Recipient Policies in Exchange Server 2003."