How to Get Higher Email Opens By Split Testing Subject Lines

Are your email open rates struggling? You might be making mistakes you don’t even know you’re making. You can find out with a split test.

Last week, we explained the power of a good split test and showed how it can be done with sign up forms and lightboxes. But split tests don’t end once your list has taken shape. You can also test different elements of your emails to see what makes for more successful emails.

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One of the easiest things to test is your subject line. Subject lines are crucial because they are the very first thing people see in their inbox. If it doesn’t intrigue them, it could also be the last thing they see of that email.

What are people testing?


ClickZ, a marketing blog, did a test (and a retest) of a consistent subject line for a newsletter vs. a subject that indicated the topic of that edition of the newsletter. The consistent subject was “Subscriber Newsletter,” and the test ensured that the key theme of the newsletter was in the first 25 characters (ie “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. There are so many variables that go into the subject that it’s important to take them all into consideration, then test them one at a time.
Some variables to consider, courtesy of The WordStream Blog:

  • 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?)

As always, even if you think you know what your subscribers like best – it’s worth the test.

Some things to consider?

There is a lot of research out there about what works and what doesn’t when it comes to headlines. Though these aren’t hard and fast rules, we want to give you some of the highlights to make your tests more effective.

What to avoid:

In short, the spam filter. A few things to steer clear of:

  • Lots of punctuation!!!!!!
  • Spammy words such as free, winner, or profits
  • Any combination of these things

Though these tactics might catch someone’s eye in their inbox, if they’re coupled with other spam concerns, they’ll be caught in the spam filter first.

What to do instead:

Convince your reader, through the subject line, that your content is worth their time and won’t take up too much of it.
According to Copyblogger, there are a few key things that accomplish this:

  • “How to” headlines
  • Headlines with numbers, indicating a list
  • Simple, direct statements
  • Headlines that sound like news, not an ad
  • The use of “you”

It’s your turn

Use these tips, consider your variables and run some tests! We’d love to hear your findings in the comments section.

Want to know more about split testing?

Check out Split Testing Sign Up Forms For More Subscribers to learn more about building your list with split tested sign up forms.

Articles in the Split Testing?Series:

  1. How Split Testing Sign Up Forms Get More Subscribers
  2. How to Get Higher Email Opens By Split Testing Subject Lines?(this article)
  3. How Split Testing Your CTA Will Boost Your Business


  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.