ADC (Active Directory Connector)

The service that replicates information between the Exchange Server 5.5 directory and Active Directory. Replicated objects include mailboxes, custom recipients, distribution lists, and site configuration information. ADC uses Connection Agreements (CAs) to define individual configurations for replication. The Exchange 2000 ADC is also used to allow Exchange 5.x and Exchange 2000 servers to coexist within the same Exchange site.

Note that two versions of the ADC exist; one for Windows 2000 and one for Exchange 2000. [Exchange 2000]