When you click the
Routing tab and then click
Routing Restrictions to configure the Microsoft Exchange Server Internet Mail Service, the following three check boxes are displayed:
- Hosts and Clients that can successfully authenticate
- Hosts and Clients with these IP addresses
- Hosts and Clients connecting to these internal addresses
If any of the preceding check boxes are selected and the host or client meets any of the selected criteria, the message is allowed for relay. For example, if you click to select two of the three check boxes, the message does not have to meet the criteria for both selected check boxes; the message only has to meet the criteria for one of the selected check boxes. Therefore, these check boxes reflect "or" requirements, not "and" requirements.
If you do set the IMS to use Routing Restrictions you must choose one of the options available in Routing Restrictions. If none of the options is selected the server becomes an open relay.
In terms of Boolean operators we do use the "or" (union) but if there is no value specified we use the set of everyone which turns the server into an open relay.