Microsoft Exchange 2000 Server connectors provide a way to create message flow between servers in different routing groups. You can use an SMTP connector, an X.400 connector, or a Routing Group Connector (RGC).
SMTP connector. Use an SMTP connector when you need to connect to an Exchange Server 5.5 site that uses the Internet Mail Service (IMS) for intersite communication. Also use this type of connector when you need to authenticate a remote bridgehead server before message exchange begins, or when you need to schedule message exchange with another server. Use an SMTP connector when you use DNS MX records, rather than Active Directory (AD) Exchange configuration data, as the basis for routing messages.
X.400 connector. The X.400 connector connects to other messaging systems that support X.400 recommendations, which were the basis of most interorganization mail exchange before the Internet took off. The International Telecommunications Union (ITU) made several such recommendations in 1984, 1988, and 1992; some of the differences in these recommendations affect message flow and interoperability, so you need to know what level of X.400 support a foreign messaging system supports before you attempt to make a connection. Exchange 2000 and Exchange 5.5 have the same level of X.400 support, and the X.400 connector is an excellent way to connect Exchange 2000 routing groups to Exchange 5.5 sites. Many large organizations that are in the process of migrating to Exchange 2000 maintain their X.400 routing network by swapping Exchange 5.5—hosted connectors with Exchange 2000—hosted connectors.
RGC. Like the SMTP connector, the RGC is SMTP-based. However, the RGC doesn't depend on DNS because the RGC is purely an internal connector that can communicate only with other Exchange servers within the same organization. Thus, the Exchange 2000 routing engine uses AD information to decide how to route messages across RGCs.
An RGC links one or more bridgehead servers in one routing group to one or more bridgehead servers in another routing group. The connector is easy to install and manage, and it takes maximum advantage of the underlying SMTP transport mechanism. Although the RGC uses SMTP to communicate with Exchange 2000 servers, it's protocol independent and uses remote procedure calls (RPCs) to send messages to Exchange 5.5 servers. (The IMS is an optional Exchange 5.5 component, so an Exchange 5.5 server might not support SMTP.) The RGC's ability to switch to RPCs helps ensure proper message flow in mixed-mode organizations.
An RGC is always one-way. In other words, you must create an RGC in both routing groups participating in a bidirectional message exchange. Conveniently, when you create a connector in a local routing group and configure it to connect to a remote routing group, Exchange 2000 prompts you to create a connector in the remote routing group as well. (Naturally, you need administrative access to the remote routing group to create the second RGC.)Configuring an RGC is painless. As Figure A shows, you need to specify the names of the bridgehead servers for the local and remote routing groups. You also need to specify the cost to allocate to the connection (the default is 1). You need to decide on a name for the connector; the name should clearly describe the connector's purpose (e.g., RGC Ireland to Hub for an RGC connector that links the Ireland routing group to the Hub routing group). Apart from these general properties, you can also configure a schedule for when the connector will become active. You can specify content restrictions, and you can permit only messages of a set priority to pass through the connector. You can elect to prevent public-folder referrals (which are the equivalent of public-folder affinity in Exchange 5.5), although the default is to permit referrals (i.e., permit users to connect to a public-folder replica outside their routing group if no local replica is found).
Within a routing group, you can restrict an RGC to specific servers so that only those servers can send messages across the connector. However, RGCs don't support connector scope (i.e., the restriction of a connector to specific routing groups within the organization), which administrators often use to ensure that only local users can employ expensive special-purpose connectors (e.g., fax connectors). Scope extends only to SMTP connectors, X.400 connectors, and the connectors that the Exchange 5.5 Message Transfer Agent (MTA) supports (e.g., Microsoft Mail—MS Mail, Lotus cc:Mail, Lotus Notes).