In the past, SPAM filters have relied heavily on a content based filtering system. Recently however, it seems that ISPs are moving towards a reputation based filtering system. Instead of focusing too much on the content of the email, they seem to care more about the reputation of the sending IP address or domain name.
So how much does content matter? Recently, I performed an A/B test with one of my customers in an attempt to answer this question. We split the subscriber list down the middle, and mailed half of the list with an image heavy email, and the other half with an html heavy email. Much to my surprise, each email received nearly an identical delivery and open rates. Website sales tracked back to each email was also very similar.
We also performed other tests such as using the word “Free” in the subject line. Again, I was surprised to find that it didn’t really affect the open or delivery rates. So does this mean content doesn’t matter any more? Not exactly. I would strongly argue that content plays a much smaller role in determining whether your email will be delivered. However, it’s important to keep in mind that it’s not possible to accurately track effects of client side email filters such as Outlook’s junk filter. Certainly, filters such as these still rely heavily on content.
I’d love to hear some feedback from anyone else’s experiences with content vs. reputation based spam filtering. Be sure to drop a comment.