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Click here for the JSpamFilter Manual section on configuring the DNSBL and SURBL settings.
When choosing a DNSBL or SURBL, be aware of the fact that these lists are maintained by private groups and that there are trade-offs involved in using them.
Some DNSBLs involve mechanical verification: ORDB, the Open-Relay Database, is one such. ORDB runs scripted, "mechanical" tests to determine whether a particular mail server is an open-relay. This is a process that admits a testing process that is completely objective: either an MTA will allow relaying or it won't. If it does, it winds up on ORDB.
Most lists typically involve some subjective determination and that's what makes things tricky. The list maintainers are, by far, reputable, concerned, civic-minded Internet professionals who are concerned about the misuse of the Internet. Yet it is the case that, on occasion, "innocent" people can wind up on the lists. We use quotes around the word innocent in that there is no crime or accusation of a crime involved here in that no offense or applicable law is being enforced by being included on a DNSBL. Thus it is actually incorrect to apply the terms guilt or innocence in this case outside of any common-sense sort of way.
List maintainers typically use numerous sources of information in coming to the conclusion that a particular mail server is sending out spam to the extent that it warrants inclusion on their list. It is the case, certainly from our experience, that the vast majority of parties that wind up on the lists belong on the lists: they've been observed sending out large amounts of Unsolicited Commercial Email (UCE), otherwise known as spam email. It is the case also that the criteria that are applied can be applied in a more-or-less aggressive fashion and it is also the case that there are claims of spamming that might not bear the burden of proof were they subject. On the other hand, these volunteers, as they typically are, a chasing a compensated, wily and mobile foe who's numbers don't seem to be diminishing and as such often have to make decisions with less than perfect data.
  • As an example, and a not-uncommon one, people can forget that they've signed up for email newsletters, or that by using one service that they are automatically "subscribed" to a newsletter. Additionally, we've all seen "Opt-Out" checkboxes that are all too easily overlooked. The upshot is that people can suddenly start receiving email or newsletters from a group, not realize that they "requested" this information...either conciously or otherwise...and then come to the conclusion that they're being spammed.
  • The vast majority of subscribers can be entirely responsible, but it can take only a few irresponsible spammers to get the ISP into bad repute with the lists. Who's right? Who's wrong? Some make the argument, often valid, that there are ISPs that aren't as vigilant about watching their subscribers as they should be. On the other hand, spammers will often be very mobile, sometimes even hijacking Wi-Fi connections while sitting in their cars and using an unsuspecting ISP client's connection to broadcast their mail.
Our general advice is that one should not use the stronger DNSBL settings like REFUSE (*) or BLOCK (!) unless one is very comfortable with and confident of a DNSBL's accuracy.
That having been said, we use DNSBLs and find them invaluable in reducing the amount of spam email. We think you will too and that you'll quickly see that using DNSBLs successfully is a matter of using common sense.
We do encourage you to please support the DNSBLs that you use!
Below are a few resources for further information on DNBSL and SURBL usage and history:

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