The Email Delivery Guru

I’ve run into two different clients recently who both were experiencing issues with content. But not exactly. Their content was getting tagged as spammy, but they were doing everything right. Perfect design, valid HTML, etc. So, what happened?

It turns out that some types of spam filters note which kinds of content receives higher spam complaints, making them more likely to filter that kind of content as spam. Meaning, if you had a bad list receiving enough complaints to cause a concern, this type of spam filter would tag your content and block you. Your content would be flagged no matter how you send it– regardless of whom you send it to and what IP address you send it over in the future.

Certain filters will do a “checksum” on your message content, and compare it to their list of checksums that generated complaints. If they note a match, your content is likely to be filtered out, and you’re going to be treated as a spammer.

This highlights how important it is to make sure you don’t send to dirty lists. This issue is fixable, and we’re working with both clients to help them address the issue, but the easiest fix is prevention. If you don’t sully your good reputation, you won’t have to undertake (sometimes severe) remediation steps down the road to get back into the inbox.
 
I assume spam filterers use tools like this to help catch spammers who do things like send their spam through hundreds or thousands of IP addresses, to bypass normal IP address reputation blocking and filtering. I also expect to see a lot more of this kind of filtering in the future. It’s just another example of how you need to make sure you do the right thing, so you don’t find yourself caught up in a trap meant to catch the bad guys.