How to Get Higher Email Opens By Split Testing Subject Lines

Subject lines are crucial because they are the very first thing people see in their inbox. If your subject line isn’t interesting or relevant, your subscribers may never open your emails.

That’s why split testing your subject lines is so important. With a simple split test, you can find out how to write more engaging subjects lines that get opened.

Ready to boost your open rates? Keep reading to learn common subject line split tests and the results from split tests run by the experts.

What are people testing?


ClickZ, a marketing blog, did a test (and a retest) of a consistent, repeated subject line for a newsletter vs. a subject line which varied each time and described the topic of that edition of the newsletter. The consistent subject line was “Subscriber Newsletter.” The changing subject line included the key theme of the newsletter in the first 25 characters (like “Prime Real Estate”).

Despite common advice that a consistent subject line helps open rates, ClickZ found the opposite:


More people were opening and engaging with the newsletter when they knew what would be covered. Though consistency was impacted by the change, the insight provided by the title allowed people to determine if it would be worth reading.

When people knew ahead of time that they would be interested in what the email had to say, they engaged more with the content as well.


Here at AWeber, we tested direct, relevant subjects against creative, sometimes ambiguous subject lines. The more direct subject lines were the clear winners. Though the creative subjects could be intriguing in the inbox, if people weren’t sure what they were going to gain from opening it, they were less likely to do so. These are the subject lines we tested, organized by style:


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The clear subject lines outperformed the creative ones in every metric. These were the numbers:


What’s the next test?

The split tests above give just a small snapshot of what’s possible when it comes to testing your subject lines. Here are even more split test ideas you can try on your subject lines:

  • Length (does shorter or longer work better for your audience?)
  • Personalization (including their name or other details in the title?)
  • Use of numbers (are they better spelled out or as numerals?)
  • Question marks and other icons (Eye catching or annoying?)
  • Humor (Do people respond well to jokes or do they prefer a straightforward approach?)
  • Scarcity tactics (Do people act on urgency?)

Want to know more about split testing?

Check out our free Minimalist Marketer’s Guide to Split Testing to learn everything you need to know to become a split testing master.


  1. Pushconvert

    6/6/2014 4:46 am

    Something about styling, I like sending my emails with the least number of styling as possible. Firstly you get better inbox rates, people don’t like to read emails with lots of graphics & it also saves time on your side.

  2. Tot Dental

    6/6/2014 8:07 am

    Definitely a great article that will help us improve our mail campaigns.
    Too often we lose this wonderful tool for not paying the attention required.
    Learn how we can get more performance is critical.
    Best regards.

  3. طراحی سایت

    6/13/2014 7:29 am

    Great article about mail campaigns. I shared it via my facebook.

  4. Damien

    6/14/2014 6:07 am

    Very good article. Thank you 😉

  5. Noah Amosu

    6/15/2014 12:53 pm

    Great tool for any serious minded marketer for publishing marketing campaigns with optimum performance and delivery.

  6. e-style

    6/17/2014 5:35 am

    I find the obsession with open rates a little confusing. Optimising your email campaigns for a great open rate is such an obvious mistake that so many companies make. If you received an open rate of 100% would you pat yourself on the back and open the champagne?…..I seriously hope not.

    Focus on your conversions and your RPE (Revenue Per Email). It’s RPE you need to optimise for, not opens.

    Running AB tests on subject lines for a couple of hours to get better open rates? That was quite sensible about 7 or 8 years ago. After 1 hour version A might be winning, 2 hours later version B might be winning and they continually swap over those first hours. Plus the winning subject line might not get the most clicks or the most sales. It really is a waste of time.

    Most people are a lot smarter than that now and are running tests for weeks, yes weeks! After at least 2 weeks, take a look at your analytics and you will quickly be able to see which has performed best in terms of conversion (RPE). What produced that high RPE? Do more of that, voila.

    Andy Francis

  7. Brandon Olson

    12/11/2015 9:47 am

    Hi Andy. Thanks for your comment. I agree that open rates are not the be all, end all. They are an important metric to track, as they can help you get more eyeballs on your email. But you also need to be optimizing your content to drive clicks and conversions.

  8. ReviewSamurai

    6/28/2014 1:57 am

    Thanks for sharing such insightful content. Subject lines are the heart of an emails. Certain subject lines might work like a wonder for one market but might not work the same for some other niche. By doing split testing it will definitely help us on finding what type of subject line works effectively for a desired niche.

    Thanks again for such a wonderful content.

  9. Rey Fernandez

    8/5/2014 8:34 am

    this is a awesome article, very informative.

    thank you.

  10. David Willden

    8/20/2014 4:21 pm

    Great tips and clear instructions.