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Content Vs. Reputation Based SPAM Filtering

by Justin Palmer - August 18th, 2007

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.

In addition, certain other practices will certainly send off red flags for the ISPs. Never use IP addresses in links (a common phising technique), forms, or javascript in your emails.

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.

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5 Responses to “Content Vs. Reputation Based SPAM Filtering” by Justin Palmer

  1. Kelly Rusk Says:

    I think while many web-based email clients have shifted to reputation filtering. Many desktop clients (or at least people using older versions) and external spam filtering software (e.g. Spam Assassin) still rely heavily on content filtering. So I think if you are mailing to strictly a B2B audience it might make a difference.

    Haven’t tested it though, so I can’t be sure!

  2. Why Your Email Marketing Can’t Survive Without A/B Testing > Palmer Web Marketing Blog Says:

    [...] the subject line doesn’t matter as much as it used to since ISPs seems to be leaning towards reputation based spam filtering. While I still avoid using all caps, I have been able to use the word free and acheive good [...]

  3. Improve your E-mail Delivery Rates - 17 Email Deliverability Tips Says:

    [...] avoid spammy words like free or using ALL CAPS. But with the shift in the last few years towards repuation based SPAM filtering, email deliverability tactics have changed drastically. Now, instead of one isolated email getting [...]

  4. 25 Email Marketing Best Practices for eCommerce Sites Says:

    [...] like “free” or “sale”. In my opinion, ISPs tend to be moving away from content based spam filtering in favor of reputation based filtering. In other words, your sending IP address and from email are more important than whether or not your [...]

  5. Seo tips and tricks Says:

    Secure Web analyzes the intent of all content entering the network – even new web pages before they have content and before they are categorized. It also protects organizations from outbound threats such as potential loss of confidential information that can leak out on all key Web protocols (HTTP, HTTPS, and FTP).

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