I was asked today if Spamcop should be "trusted." After all, even the Spamcop Wikipedia page says that their blocking list is "controversial." Though, is it truly more controversial than any other blacklist out there? Let me tell you what I know.
The last time I looked at Spamcop from a receiver's perspective was back in 2007. Back then, I found it to be pretty accurate. A Spamcop listing truly seemed to be indicative of a sending IP address sending unwanted mail. That data is from a long time ago, but I haven't seen anything since then that would make me think they've changed for the worse by any significant measure.
Long, long ago, when Spamcop was a one-man show (created and run by a guy named Julian Haight), I did find the blocking list to be controversial. I regularly saw listings of IP addresses sending very clearly only opt-in email, with nothing funny or weird going on. Even confirmed opt-in email. But since that time, Spamcop has been sold to Ironport, who has since been sold to Cisco. So nowadays, Spamcop is a tiny little part of Cisco. With that transition to corporate ownership, came new hands and new policies, which (in my opinion) seemed to significantly improve the reliability of Spamcop.
From a sender's perspective, I regularly help clients monitor for and address Spamcop listings. Because my prior testing of Spamcop led me to trust that it was typically correct, I typically think that a Spamcop blacklisting of a client's sending IP address is probably "correct" -- I suspect it is properly indicative that there is a problem that needs to be addressed. I think if a sender is regularly finding themselves listed on Spamcop's blacklist, then their list is probably outdated, poorly permissioned, or otherwise flawed. In these cases, I do think it's appropriate to run a permission pass to clean up the list and resolve any list hygiene issues. At the same time, discard any list segments that contain anything other than opt-in subscribers. Bought list? It's time to throw it out.
That's my opinion, provided with my alternating "sender" and "receiver" hats. What's your opinion?