How to work with email spam blacklists

Spam! (freezelight@Flickr)

On the one hand, anti-spam blacklists are extremely useful. On the other, they can be fantastically irritating. How can you choose a good one for cleaning your incoming email? And how should you react if your email server gets blacklisted? Here's how, in The Long View...

Email blacklists -- also known as blocklists, DNSBLs, RBLs, or the more general "reputation services" -- allow spam filters to identify known spam senders and cut off the email connection. They are a quick and efficient way to reduce spam -- typically by as much as 80%. However, not all blacklists are created equal. Some are run badly, which can cause you to lose legitimate email -- so it's important that you only subscribe to well-run blacklists in your spam filter. And if you're an email sender, the last thing you want to hear is that your outbound IP address has been included in a blacklist. Read on for my top tips on how good blacklists are run; it'll let you avoid the bad ones and help you work with the blacklist operators if you get incorrectly listed... The Anti-Spam Research Group (ASRG), a working group of the Internet Research Task Force (IRTF) is wrapping up its latest set of guidelines for blacklist best practices. As with all IRTF activities, the ASRG focuses on longer term research issues than those tackled by the better-known IETF. The current draft of the guidelines seems to have rough consensus within the group. While it's poor form to treat these drafts as a "standard" or anything other than a "work in progress," it does contain some excellent advice on how a good blacklist should be chosen and run. Here are some of the best bits, mixed in with my own favorite tips. Advice for users of blacklists

How should we choose a blacklist? A good blacklist operator...

  1. Clearly states the list's intended use (e.g., it's inappropriate to use some lists to block connections without further corroborating information).
  2. Clearly, coherently, and transparently states its listing criteria and aggressiveness of listings.
  3. Clearly, coherently, and transparently states its delisting policies and offers a Web page to request delisting.
  4. Maintains an audit trail of listings and delistings, preferably a publicly-searchable one.
  5. Isn't afraid to share its demographics, so potential users can tell if similar sites use the list.
  6. Is well regarded by knowledgeable users.
  7. Clearly and consistently communicates announcements, such as policy changes, future planned outages, or current problems.
  8. Provides a well-documented, automated way to test if the blacklist is operational (in the past, some blacklist operators that gave up simply listed the entire Internet as a spam source, in the hope that people would stop querying them).

Controversially, some blacklists charge a fee for delisting, or for expedited processing. The ASRG strongly recommends against this practice, because it runs the risk of a conflict of interest -- even to the extent of being a protection racket. However, the opposing point of view is that this is simply a different business model; some go so far as to see this as a political point about regulation vs. market freedoms. Advice for bulk email senders

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