The check_relay ruleset in the sendmail.cf configuration file for UnixWare 7 sendmail(1M) can be configured to reject mail based upon the MAPS (Mail Abuse Prevention System) Realtime Blackhole List maintained at maps.vix.com. The MAPS RBL is a list of sites which are known to either originate or relay spam. During an SMTP session, check_relay makes a DNS query on the IP address of the connecting host to check for the existence of an address resource record (``A'') of that host under the rbl.maps.vix.com node. If such a record exists, then the check_relay ruleset issues an error and drops the SMTP connection.
The check_relay ruleset follows the following algorithm:
Mail from <connecting host> refused by blackhole site rbl.maps.vix.com
By default, this feature is disabled in sendmail.cf. To enable check_relay, set the Check_Relay macro to a non-null value by changing the following line in sendmail.cf:
to the following:
Next, stop and restart the sendmail daemon to load the configuration
changes by executing the following commands: