The MAPS (Mail Abuse Protection System) RBL (Realtime Blackhole List) was the first application of a way of using a DNS list as a means of identifying hosts that have been associated with the sending of spam mail. A full description of the service and the technology and ethics behind it can be found at http://www.mail-abuse.org/rbl/ along with more general mail policy information at http://www.mail-abuse.org/.
+The MAPS (Mail Abuse Protection System) RBL (Realtime Blackhole List) was the first application of a way of using a DNS list as a means of identifying hosts that have been associated with the sending of spam mail. A full description of the service and the technology and ethics behind it could once be found at http://www.mail-abuse.org/rbl/ along with more general mail policy information at http://www.mail-abuse.org/.
In the few years since MAPS started operating, other similar services although with different aims, procedures and reliabilities have been introduced - MAPS itself has a number of these (ie MAPS/DUL which maintains lists of dial up modems). At this point in time there are many 10s of services with varying charters - lists of these can be found at http://relays.osirusoft.com/ and http://spamblock.outblaze.com/spamchk.html. The services are now normally referred to as a DNS Block List (DNSBL), rather than RBLs, however you will find that earlier Exim documentation (ie for version 3.x) will use the older term.