You can prevent the connection of users who might abuse your e-mail server.
Unwanted users might connect to your server, and send unsolicited mail. This unsolicited e-mail takes a great amount of central processing unit (CPU) cycles and space. Also, if your server allows others to relay unsolicited mail, other servers might block the mail that comes from your server.
You can specify IP addresses of known unwanted users, or you can connect to a host that contains a Realtime Blackhole List (RBL) server. These Realtime Blackhole Lists provide a listing of known IP addresses that send unsolicited mail. See the Mail Abuse Prevention System (MAPS) LLC Web site for an example of a host that contains a Realtime Blackhole List.
To specify known IP addresses or a host with a Realtime Blackhole List, complete the following steps: