How to Get Around the Outlook Junk Filters

Recently, we were preparing a series of emails to go to a very large list for a client. We had completed the design, coding, rendering and delivery tests, and all was great except for getting through the Outlook 2003 and Outlook 2007 junk filters. Typically, all of the process and best practices we employ lead to no problems by the time we get to this point, but not this time. I thought the following process would be of interest to FulcrumTech’s readers in terms of how we solved this tough spam issue with Outlook:

  1. We reviewed all content to ensure that no words, phrases, or other language known to be problematic had crept into the email out of context. You can see a current list of such words used by Outlook’s filters at This is very tricky because I am not convinced that the words listed here are, in fact, all of the words that the filter is checking against. If you think about it, if Microsoft published the complete list, it may just make it that much easier for the real “bad guys” to get around the spam filters. We didn’t have any of those words or phrases, so that didn’t solve the issue.
  2. Next, we used several commercial spam checking tools. We started with the commercial spam-checking tool associated with the email service provider we were using for this project. Again, nothing indicated to be a problem. So, we used several other commercial tools – again, no problems were uncovered. They all indicated the email was clean.
  3. We then turned our attention to the subject line. While the subject line was quite innocuous, we tried many variations to see if anything worked. Nothing solved the problem.
  4. We analyzed the underlying html code to ensure no inappropriate characters or missing end tags existed. We found nothing. As a precaution, we recoded the entire email using a different coding strategy. That did not make a difference.
  5. In an attempt to isolate the problem, we removed pieces of the email, one piece at a time to determine what element(s) may be causing the problem. No single element of the email appeared to be causing the problem – not the title, the main body, or footer.
  6. Finally, we began working with a variety of permutations, as our hunch was that we had multiple issues working concurrently. While we didn’t have any “bad” words, we did use the word Free, but not frequently to make a difference on its own. While we hadn’t uncovered any perfect subject lines, we anticipated that in combination with changes to the code, we may be able to uncover an option that could work. Ultimately, we came up with a subject line in combination with the new code which worked! Clearly, we had multiple factors working together which was causing the issue.

It is not uncommon to see these types of problems, and usually, changing a few words or a subject line can make the difference. When you have a really tough challenge as we had, you’re going to need to start working through permutations until you find one that works. Unfortunately, the ISPs and filters don’t necessarily tell you everything about how their filters work, so testing is critical. I will also add the importance of tracking the email reputation score (see, which is another important factor in getting your emails through the filters.

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