Spamhaus provides a set of managed block lists to assist with identifying and blocking IP addresses and domain names that are likely to send out spam or cause malware infections.  These lists are available via the spamhaus.org web site as well as via the DNS-based Block List (DNSBL) standard.  To limit the load on their infrastructure, Spamhaus only permits users to query the service for non-commercial purposes and sets a cap on the number of daily queries allowed.

As of August 2016, due to the fact that Steadfast is a commercial business and has a high volume of DNS traffic, Spamhaus has requested that we reject all queries to the DNS block lists via our public resolvers.  This means that instead of fetching a usual DNSBL response code, the resolver will return NXDOMAIN, which indicates no result is available.  This response should not cause any issues for mail servers using Spamhaus services, except that they will no longer be able to use the block lists for filtering email.

We cannot grant exceptions to the query restrictions on our public DNS resolvers.  It is not possible for Steadfast to meet the usage terms of the free DNS feed and we cannot reasonably meter the usage of the paid feed to provide a bundled version to our customers.

If you need the data from Spamhaus as part of an anti-spam effort or product, you have two options.  You may either run a DNS resolver locally on your server to query the DNS block lists directly if you meet the free feed criteria, or you may contact an authorized Spamhaus reseller to gain access to the paid version of the data feed intended for commercial use and high-volume consumption.

For more information on the data feed and its restrictions, please see the following web site:

• https://www.spamhaus.org/organization/dnsblusage/

If you have questions about how to run a local DNS resolver, please feel free to contact us.