DNSBL.info was started in 2002 to provide a single website where visitors could check an IP address against a list of know DNS based blacklists. Each blacklist runs independently to provide a list of IP address the match the listing criteria of the maintainer. Mail server administrators choose to consult these lists to aid in their determination of whether or not to accept incoming mail or flag it to their users as possible spam. As part of the process of running a blacklist check service we created an experimental blacklist for internal use. This experimental blacklist, spamsources.dnsbl.info, was discussed on a number of spam related discussion lists. Unfortunately a number of blacklist monitoring services picked it up and included it in their list of dnsbls checked.
Prior to 2009 we concluded our testing of the blacklist and ceased returning responses to queries. Since then queries to the non-existent blacklist have continued in excess of 15,000 queries per second. In an attempt reduce the load on our servers we announced in January 2010 that we would start returning 127.0.0.2 to all queries. Hopefully this would alert any mail server administrators that were still consulting this list by indicating that our blacklist suggested that ALL incoming mail connections were suspect. This would hopefully alert those mail administrators that put an experimental blacklist into their production environment. We understood that this implementation could cause unwanted impact and we delayed implementation until January 2011.
We are now in the process of attempting to alert blacklist monitoring services and mail administrators that might erroneously still be checking against our former list. We've completed the first round of notifications to the blacklist monitoring websites. Unfortunately we have no way to contact mail administrators that continued to check our former blacklist. The only way that we can further reduce the queries to our servers is to start periodically serving up results that will alert blacklist monitors and mail server administrators. The length of time and frequency of these listings will increase till we're serving these results 100% of the time.