The Microsoft articles "XCON: Connector Delivery Restrictions Do Not Work Correctly" (Q277872, http://support.microsoft.com) and "XCON: Restriction Settings Are Not Applied After Configuring the Delivery Restrictions Option" (Q279813, http://support.microsoft.com) explain that restrictions you place on SMTP-based connectors (i.e., the Routing Group connector and the SMTP connector) don't take effect until you also add a registry value. Let's look at how to use the Exchange 2000 Server UI to create restrictions and how to fully implement the restrictions.
Applying Restrictions
As Figure 1 shows, the Delivery Restrictions tab on an Exchange 2000 connector defines the users from whom the connector will accept or reject messages. To access the Delivery Restrictions tab, open Exchange System Manager (ESM), select a connector, and view the connector's properties. For the default set of Exchange 2000 connectors, the Message Transfer Agent (MTA) controls the restrictions placed on the X.400 connector, and a combination of the routing engine and the SMTP service controls the restrictions on routing-group and SMTP connectors. As you can see in Figure 1, you can use individual mailbox names or distribution groups to define who can use a connector. . . .
Dan Benjamin October 25, 2002