The Windows 2000 Active Directory Connector (ADC) and the ADC versions in Exchange 2000 Server's beta versions and early release candidates (RCs) let you synchronize an Exchange Server 5.5 mailbox to a contact, a disabled user, or an enabled user object in Active Directory (AD). Although this capability provides great flexibility, it's also dangerous. If duplicate objects occur in AD and you've used the ADC to create contacts, matching might be imprecise and potentially fraught with problems.
The ADC that ships with the release to manufacturing (RTM) version of Exchange 2000 (build 4417.5) is less flexible but, in essence, better. Now, the ADC lets you create only disabled user or enabled user objects, not contacts; therefore, the problem of matching based on names becomes moot.
However, the exception to this rule is that the restriction on contacts applies only to intraorganizational connection agreements (CAs); interorganizational CAs can create contacts. An intraorganizational CA links an Exchange Server 5.5 organization that shares the same name as an Exchange 2000 organization (i.e., a mixed-vintage organization). Conversely, an interorganizational CA synchronizes Exchange Server 5.5 mailbox data from one (or many) organizations into a differently named Exchange 2000 organization. For example, you have an Exchange 2000 organization named North, and you want to synchronize in objects from an Exchange Server 5.5 organization named South. To accomplish this synchronization, you must use an interorganizational CA.