Why don't spam blocking lists block only the spammers?
A Frequently-Asked Question



Block list WELISTEM has listed our upstream provider, and the listing includes our IP addresses. We can't speak for our provider, but we are extremely against spam, we have never provided any service of any kind to any spammer and never will, our AUP prescribes a fine the size of the national debt for spamming, we're responsible for jailing 6,174 spammers, we received the 2003 Spork Magazine Anti-Spam Award Of The Year, and most of all, We Hate Spam As Much As The Next Guy. Why doesn't the WELISTEM list restrict its listings to include only the spammers?

There are several reasons why blocking lists might list generous amounts of netspace.

1. Chances are good that your provider has been providing service to one or more spammers, and ignoring complaints about them. Most blocking lists start out by listing a single IP address, only expanding the listing when they are sure that complaints have been received by the provider and that no satisfactory action has been taken to resolve the complaints.

2. History tells us that a provider that will ignore complaints about one spammer will acquire more spammers, and will take no discernible action against the new spammers. Spammers tend to communicate, and they gravitate to the providers they believe will allow them to spam with impunity. Currently unallocated space controlled by such a provider has a better-than-even chance of being allocated to more spammers in the near future. Whatever the providers' reasons may be for knowingly continuing to provide services to spammers, the fact that they do so now indicates that they will continue to do so.

3. Spammers do not want to buy pre-blocked IP addresses. The spammers who will naturally gravitate toward a spam-friendly provider will decline to buy services from the provider whose space is not usable for e-mail. For purposes of stopping spam, this is almost as good as convincing the provider to stop providing spammer support services.

4. You probably have no contractual right to the particular IP address you are using; few contracts stipulate such a right, while most contracts allow a provider to make changes to your service at their whim. In short, there is nothing keeping them from moving you to a currently listed address space within the netspace they control, and moving a spammer into the currently unlisted address space you occupy now. (If there is something preventing this, the world has no evidence of it.) This would allow the newly-situated spammer at least one unimpeded blast at the world, and leave you listed instead of him. There is at least one well-documented example of this scenario; there are hundreds of examples of spam-friendly providers moving their spammers from address to address to help them elude blocking lists.

5. You may be sharing an IP address with a dozen other virtual-hosted domains. (Perhaps not, but how can anyone else know?) No one has any reason to believe that your provider won't move ten spammers onto the same IP address you use; there is reason to believe your provider may be acquiring more spammers, and there is no reason to believe your provider won't put them onto the IP address your system occupies.

6. Keeping careful track of your provider's spammers and non-spammers leaves the blocking list maintainer doing all the work, and the spam-friendly provider and their spammers getting the lion's share of the benefit. The provider can sell to any spammer he wants without hindrance, and the new spammer gets at least one free spamming run for each time he can get the provider to give him a new, unlisted address. Listing the provider's netspace instead of just the spammers' addresses means minimum work to the blocking list maintainers and maximum benefit to the list users, and redirects the problems to the provider and their customers. You become a victim of the evils which you pay your provider to tolerate.

7. When a blocking list lists only the spammers, new spammers are discovered only after dozens of thousands of people receive spam from them. The purpose of a blocking list is to enable its users to block spam before it arrives, not to close the barn after the horses have left. Listing the space of a provider who willingly hosts spammers, space in which spammers already reside without visible penalty, is only taking preemptive action to point out the extra spammers that history suggests will soon arrive.

8. Some people believe that blocking lists list more than just the spammers in order to encourage non-spamming customers to complain to the provider about their spammers. By the time innocents are listed, it has become obvious that complaints from non-customers are ignored; those who believe in this negative reinforcement theory hold out the hope that complaints from customers might have some effect. Often, the innocent customers of a spam-friendly provider are unaware that their provider is spam-friendly until the moment they find themselves listed.

9. History shows that listing only the spammers does precious little to stop the spam. The results of several earlier attempts show that listing only spammers simply doesn't work as effectively, if indeed it can be said to work at all.

10. Remember that the system administrators who use blocking lists use them because they trust that using the list will eliminate a maximum of spam while blocking a minimum of wanted e-mail. Admins who find that a blocking list is not working that way will stop using it. Most likely the list in question affects very little non-spam e-mail.


In short, your provider may have every intention of running a spamhaus, while you innocent victims just want to run your net-friendly, non-spamming domains. Problem is, your provider owns and controls the IP addresses, so your provider wins. The innocents can continue to support the spamhaus with their dollars, and fantasize that the spam will abate enough that their addresses might be unlisted; or they can find responsible providers who protect the Internet by shunning customers who might get them into blocking lists.






Disclaimer: The author has no connection with any blocking list other than his own private list. The author has no connection whatever with any DNSBL except as a satisfied user. The author also maintains a boycott list which is available on the web, but it is not recommended for use as a blocking list. This material describes the perceptions of a long-time spamfighter. If anything here contradicts reality, let me know.