Service’s zone: dnsbl.spfbl.net
It is noteworthy that, in the case of returning 127.0.0.3, we flag all IPs which we consider unsuitable for hosting mail transfer agents. In that case, the DNSBL does not only list systems that send spam, so it’s up to each administrator to decide how to use it. Making an analogy with the RFC Ignorant list (now RFC Clueless), we also require a number of important settings, so we could be called the “SPF ignorant” or “FCrDNS ignorant” system. In addition, any machine with no purpose of email service is a potential vector of a hacker attack, so this flagging also prevents any possible attack rather than waiting for the first damage to blacklist the IP after the injury caused. More about our rules, in the our delist page.
IMPORTANT: We do not provide any guarantees, despite the best efforts to maintain a stable and coherent system. Use at your own risk and take into consideration that our systems works based on reputation, without privileges to any system, including Internet providers and email marketing systems, if they have a poor reputation. For this reason, we suggest you use our DNSBL to mark emails as spam, rather than by rejecting emails. Check your MTA documentation for details or, if it is not feasible, consider use SpamAssassin or Rpamd.
IMPORTANT: Current limit is 10 queries per second and the response will have rcode 5 (REFUSED) when reached. Higher frequencies require contribution. Please contact us informing your IP or range, for further details. Even within the query threshold, consider making a donation so we can maintain and expand our free services.