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.

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:



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:

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:

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:

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
Katie Pilot was a Marketing Intern at AWeber.

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  1. 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.

    6/6/2014 4:46 am
  2. 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.

    6/6/2014 8:07 am
  3. Very good article. Thank you ;)

    6/14/2014 6:07 am
  4. 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.

    6/28/2014 1:57 am
  5. this is a awesome article, very informative.

    thank you.

    8/5/2014 8:34 am
  6. Great tips and clear instructions.

    8/20/2014 4:21 pm