A/B Email Testing: Turning Good Emails Into Great Ones

Not sure which subject line will work best in your email? Wondering what the best CTA will be? Why not try A/B email testing?

a/b email testing

A/B email testing is a necessary tool in an email marketer’s kit. It’s a way of checking your intuition and gauging your audience's reception. You might have heard of A/B email testing, referred to as split testing. It’s a method of testing one version against another by making small, controlled changes to the content or the sending style. When these tests are measured and reflected on, it can create more powerful, better-converting emails.

If you’re reading this as a business owner or a marketing lead, you should already know the power that email marketing can have. It’s one of the best methods of outreach available. You can send direct, personalized, tailored content that resonates with the recipient. This is a method of communication that is unparalleled in that regard.

It’s little wonder, then, that email marketers want to get their campaigns right. They want to position them in the best way, with the best content, so that they receive the best results. This is where A/B email testing can help.

In this article, we will explore precisely what A/B testing entails. We’ll consider the various aspects of an email you should test. Plus, we’ll guide you through how to conduct a test yourself. 

  • Best practices for A/B email testing
  • How do you measure the results when conducting an A/B test?
  • What variables should you change when testing?

Understanding the Basics of A/B Email Testing

Imagine that you’re writing a marketing email. You’ve pulled together all the content but can’t decide which subject line would be more effective for the target audience. You’ve got subject line A and subject line B. How do you find out which is more effective? You run an A/B test. 

The aim is to find out which receives the best reception so that it can become the preferred option for the campaign at large. Following the conclusion of the test, you interrogate the metrics and see which gave the better results.

The important element of A/B testing is ensuring it is a controlled test. That means changing only one variable at a time. So, if you want to test how effective a subject line is, as in our example, that is the only thing that changes. The content remains the same in both emails. As does the call to action, the signature, the greeting, and everything else. By keeping it simple, you can accurately pinpoint the variations in performance.

Key Elements to A/B Test in Emails

split testing

Subject Lines

This is your first impression. It certainly counts. It’s your chance to convince the recipient that the contents of the email are worth reading and they should click through. Testing different subject lines can have a dramatic effect on open rates. Some audiences react better to formal, informative subject lines. Others prefer a more creative, curiosity-based subject line. Play with lengths, tones, language, and emoji use.


The actual body of the email is slightly harder to test as it naturally contains lots of variables. That said, you can get across the same information and message but with a varied tone or style. You could include a story-telling element or humor. You could test long-form versus short-form content. It’s a good test of what keeps an audience engaged and willing to stay with an email.


The call-to-action is one of your best conversion opportunities. Some are simple sentences within the body of the main content. Others are styled as buttons. There are many variables to change, so be wary of changing too much at once. Change the style of the button but not the text and vice-versa. Experiment with directness. Does a more casual “Learn More” work better than “Book Now”?

Email Design

Changing email design is another variable you could alter. There can be stark differences between image use and just plain text. Graphics or not. Changing the amount of white space can also have a considerable impact depending on the audience and the way they perceive it.

Sending Time

Rather than changing the actual email itself, you can change the time that it is sent. Different audiences and industries react to emails better or worse depending on when they are received. Some industries even have the best time to send emails. Try sending it on different days or at different times of the day. As with other tests above, avoid changing both the time and the day. Change one aspect of the variable for accurate results.

How to Set Up an A/B Email Test

  1. Define the Objective: Consider what you want to understand from the test. Do you want to increase click-through rates, conversions, or open rates?
  2. Pick Your Single Variable: Select one, and only one, variable to test.
  3. Create Your Variants: Create the two variants within two different emails.
  4. Segment Your Audience: You could do this on a small section of your list, but larger samples give more accurate results. Split them into two random but equally sized groups.
  5. Send and Track: Send the email and monitor the results (if you’re testing sending time, schedule the sending times).
  6. Analyze: Once the test is completed (after a specified period of time), analyze the results from that snapshot and look into the metrics.
  7. Adapt and Adopt: Change your campaign based on what you’ve learned, implement the successful variable, or run another test.
  8. Iterate: Continue to run tests on different variables as the campaign progresses.

A/B Email Testing Key Metrics

  • Open Rates: The number of emails sent that are opened by the recipient. This is a good indicator for sending time and subject line.
  • Click-Through Rates (CTR): How many recipients (as a percentage) click on a link in an email? Useful to measure CTA effectiveness and the persuasiveness of the body.
  • Conversion Rates: Similar to CTR, but rather than just clicking, this measures how many people complete the desired action. A higher conversion rate means a more effective email overall.

Key Takeaways

A/B email testing has the opportunity to exponentially increase the effectiveness of your campaigns. Once you’ve found that one element is more effective than another variable, include it in your email. Then, test something else. Once that’s done, test something else. The testing continues until you achieve something that converts almost every time. And that will take a whole lot of testing.

  • Consider your test results holistically. Try to understand what they mean in regard to your audience's macro preferences.
  • Keep an eye on email trends and see if they are effective with your audience.
  • A/B testing is an opportunity to rely on facts rather than guesswork.

A/B email testing is just one of the features available in Instantly. Why not see for yourself and get started for free today?