What is the SBL?
The SBL (Spamhaus Block List) is a “blackhole list” a service that provides a way to detect and bounce incoming spam. Blackhole lists do this by comparing the machine that is sending mail to a list of sites known to be major sources of spam. Most blackhole lists concentrate on blocking mail from “open relays” (mail servers that are configured in such a way that they may be used to send mail from anywhere to anywhere else). This approach, unfortunately, has a high rate of improperly bounced mail since many open relays are also used to process legitimate mail. The SBL takes a more conservative approach by concentrating its efforts on bouncing mail from sites that appear to do nothing but transmit spam. For more information on the SBL, see The Spamhaus Block List FAQ.
