Spamcop BL: Take Another Look (It’s Accurate!)

If you know me, you know that in the past, I’ve made no secret of my disdain for the Spamcop DNSBL, aka the SCBL. I’ve worked in spam prevention, deliverability, and the email realm for a long time, in various capacities. I’ve created and run at least two blocking lists that you know about. Later, I helped to design and create a system that processed thousands of confirmed opt-in/double opt-in newsletter signups a day. Combine those two details together and that’s what led me to take issue with Spamcop. My employer’s COI/DOI signup servers kept getting listed by Spamcop, based on some really bad math to measure email volume thresholds and make a determination as to what to list.

I was trying to do the right thing. I was implementing what Spamcop (and other anti-spam groups) want: confirmed opt-in/double opt-in. Yet Spamcop was listing the servers and subsequent mailings regardless. It made me really frustrated, and I was very disappointed. See, it’s not really fighting spam. It’s just blocking mail you don’t like, or don’t care about. While perfectly allowed, I am of the opinion that it’s lame to do so under the banner of “fighting the good fight” to stop spam. I’ve shared my thoughts on this topic in just about every available forum—websites, blogs, discussion lists. I know I’ve personally guided many sysadmins away from using the SCBL in the past, because it was easily, demonstrably, listing things that were obviously not spam.

In February 2007, I found that Microsoft was using the SCBL to filter/reject inbound corporate email. (Note that I said corporate email—mail sent to users at micrsoft.com, not users of MSN or Hotmail. I don’t know whether or not SCBL data is used in MSN Hotmail delivery determination, but from what I’ve observed, it doesn’t seem to be.) This started me off on another rant on how ill-advised I felt this was, based on my prior experiences with Spamcop. Some kindly folks (and some less kindly) suggested that I needed to revisit my opinion of the Spamcop blocking list, because things have changed.

After a lot of measuring and discussion, I’m here to tell you: Spamcop’s DNSBL has changed, and for the better. It works very well nowadays, as personally measured by me. The open question on Spamcop was what drove me to dive into my massive DNSBL tracking project. I started that back on March 10^th. Ever since then I’ve been compiling data on Spamcop blocking list matches against both spam and non-spam. Here’s what I see:

DNSBL	Spam hits	Acc %	Ham hits	Failure Rate
Spamcop SCBL	156194	49.37%	0	0.00%
Spamhaus ZEN	255521	80.77%	5	0.10%
Spamcop+ZEN	267795	84.65%	5	0.10%
Range:	~ 74 days
Total Spam	316348
Total Ham	4999

As you can see, Spamcop helps you attack nearly 50% of spam received, while affecting no legitimate senders. Very few lists do better. Spamhaus ZEN (which combines multiple lists) does better, but will occasionally have a false positive, based on some reputational issue perceived with a given sender.

My recommendation: Spamcop’s blocking list is safe to use, and will effectively help you reduce the amount of spam you have to deal with. Where I find it particularly useful is as an addition to Spamhaus ZEN: If you block mail from entities on either list, you get a 3.8% percent boost in effectiveness. Meaning, just under four percent of my spam hits are found on the Spamcop list, but not on Spamhaus.

For historical reasons only, here are links to my previous articles on Spamcop:

Spamcop Roundup http://www.dnsbl.com/2007/03/spamcop-roundup.html Spamcop BL: A blocklist with a hair trigger http://www.dnsbl.com/2007/02/spamcop-bl-list-with-hair-trigger.html Microsoft using Spamcop BL http://www.spamresource.com/2007/02/microsoft-using-spamcop-and-spamhaus.html My Problems with Spamcop http://www.spamresource.com/2003/03/problems-with-spamcop.html

Spamcop Roundup

5/22/2007: This information is out of date. Please click here for my latest take on Spamcop's SCBL.

My most recent take on Spamcop, from February 2007, can be found here. In that commentary, I talk about the history of the Spamcop spam reporting service, its current corporate ownership, and my take on how this type of DNSBL works, especially as to how it relates to to the impact against solicited (wanted) mail.

In February 2007, I found that Microsoft is using Spamcop to filter inbound (corporate) mail. By corporate mail, I mean mail to microsoft.com users, not mail to MSN/Hotmail users. This surprised me, because of what I believe are aggressive listing practices on the part of Spamcop. Indeed, how the issue was brought to my attention was by an unhappy person mad because he couldn't send one-to-one mail to Microsoft, because Spamcop blocked it.

Also, back in 2003, I published an article about the ongoing issues I was having with Spamcop blocking opt-in confirmation requests. Back then I found (through some admittedly unscientific survey techniques) that admins using the SCBL seemed to assume that all blocked mail must be spam because Spamcop blocked it. Not a very encouraging find. It was also a bit insulting to be lectured on how confirmed opt-in worked by people who were blocking confirmed opt-in requests, especially considering I've been pushing senders to implement and utilize confirmed opt-in/double opt-in for many years.

Spamhaus ZEN: Recommended

Look for a longer article from me in the near future on Spamhaus; I'm collecting a ton of data against a large spam corpus and hope to summarize and publish my findings within the next month or so.

Until then, feel free to bop on over to Spam Resource, where I talk about my experience using the Spamhaus ZEN list to tag and filter inbound mail to our abuse desk. I've been quite pleased with the results.

Also of note is that Microsoft is using both Spamcop and Spamhaus to reject mail to their corporate users. (They're NOT using it on MSN Hotmail.)

Update: Find my full review of Spamhaus ZEN here on DNSBL Resource.