Cold Email · · 5 min read

Cold Email A/B Testing Best Practices

Understanding necessary email A/B testing best practices will help you achieve the best results. We explore the ins and outs of the process.

email a/b testing best practices

There’s more to email A/B testing than comparing one idea against another. It’s an opportunity to get inside the heads of your recipients. It’s a chance to understand what impresses them and what they like to engage with. You gain insights into customer preferences. Insights that will lead you toward making more effective communication.

In this article, we’ll share the ins and outs of A/B testing. That will include the best practices that you should be employing as you conduct email testing.

  • Why is email A/B testing important?
  • Should you have a hypothesis before testing?
  • How do you measure A/B test success?

A/B Testing and Cold Email 

A/B testing is a way of getting an idea of what might work in the future. The process involves taking two slightly different versions of an email and sending them to two segments of the campaign. The results are then analyzed, and insights are found. This data then influences how the campaign is developed moving forward.

The A/B of the testing refers to the two versions. A is the control (the original), and B is the variant (the slightly altered version). The important part of A/B testing is that only one element of the email is changed. That could be the tone, the subject line, the images, the signature, or the call to action. There are other elements you could change, but only one can be changed per test.

There’s precision in the simplicity of the test. The singular focus makes it incredibly simple to pinpoint which variant the audience prefers. You gain a result and actionable data very quickly. Especially when compared to multivariate tests.

Why Bother With Email A/B Testing?

The immediate answer to this question is because it’s essential. It’s a method that everyone sending marketing or sales emails should be employing.

By carefully measuring and testing their audience, marketers and salespeople can better understand who they’re talking to. The headline metrics are certainly head-turners. Seeing cold email open rates rise and click-through rates improve is very welcome. It isn’t, however, the only aim.

The holistic goal is to foster a deeper connection with your audience. You get to enhance that connection and develop a better customer experience. When you launch a new campaign, what are you basing your content on? A hunch? Intuition? Guesswork could go well for you, but just as easily, it could fail. Removing guesswork and replacing it with hard data makes for a far more confident campaign. By the time you’ve tested every aspect of your email, you’re well on the way toward perfection.

Email A/B Testing Best Practices

Consider these best practices if you want to succeed with email A/B testing. Adhering to them will produce the most effective tests, with results to complement them.

cold email a/b testing

Test One Variable at a Time

We’ve mentioned it above, but this really is the most important best practice. Only change one variable at a time. If you change more than one, then you have no idea which change caused the variation in success. That means if you’re going to change the subject line of the email, the entire rest of the content remains the same.

Choose a Significant Sample Size

When conducting your tests, you need to get the right audience size. Pick a group that is too small, and you won’t have a clear enough picture. If you go for a group that’s too large, you’ll reduce the cost-effectiveness and use too many subscribers in the test. To genuinely A/B test, you should have a list with at least 1,000 subscribers. 

Randomize Your Segments

Once you’ve selected your sample, the segments must be completely random and devoid of any bias. By segmenting at random, you ensure that groups A and B genuinely represent your list.

Set Clear Goals and Metrics

Give yourself some clear goals and choose the metrics you will track. One should inform the other. Ask yourself some questions to help. Do you want more conversions? Do you want a higher open rate? Would you like more responses? Your answers should indicate your goals and then your metrics.

Give Your Test Sufficient Time

It’s important that you set a period of time for your test to run and then stick to it. There’s a balance to be had here. Too short and you may not receive enough data. Too long and your recipients may begin to be influenced by external factors such as market shifts or holiday seasons.

Analyze Results and Implement Learnings

Once the test is completed, it’s time to analyze the data. The headline email marketing metrics are important and give you a clear indication, but they’re not the end of the learning. Spend time questioning why you’ve achieved these results. Why do you think consumers have reacted the way that they have? When you reach a conclusion, you can take your findings and implement them into your email marketing strategy. 

Keep Testing and Optimizing

Email A/B testing isn’t a one-time task. There should be a mantra of continuous improvement. If you successfully test one variable, then move on to the next. If you come up with a new idea or spot a new trend, then you should A/B test that against your current work. This should be your continued quest toward perfection. 

Developing a Hypothesis for Email A/B Testing

Before you can begin a test, you should take a guess at what the outcome might be. Which variable do you feel will be successful, and why do you think that is? This is called a hypothesis. By creating one before the test, you’re better able to test your strategy. Plus, it helps when you come to draw conclusions once the test has finished.

Your hypothesis should have three specific characteristics. It should be specific, testable, and align with your marketing goals for the business. You don’t necessarily need to write it down, but you should at least ask yourself these three questions:

  • What are you going to change?
  • Why do you think it will make a difference to your campaign?
  • How does it match with your broader marketing objectives?

Answers might be: We will change the subject lines because we feel it will increase open rates. We’re doing this to improve user engagement.

Picking a test that matches your broader marketing goals ensures that the tests have a purpose. Testing for testing’s sake isn’t worth your time and effort. Instead, you should only run A/B tests when you feel the outcome will have a tangible and noticeable impact on future campaigns.

Selecting and Understanding Metrics




Open Rate

The percentage of emails opened by recipients.

Measures the initial appeal of your email.

Click-Through Rate (CTR)

The percentage of recipients who clicked on a link in the email.

Reflects engagement and interest in your content.

Conversion Rate

The percentage of recipients who took the desired action. (Replied / Booked / Bought)

Indicates the overall effectiveness of the email.

Bounce Rate

The percentage of emails not delivered.

Helps assess the quality of your email list.

Unsubscribe Rate

The percentage of recipients who opt out of your list.

Signals content relevance and recipient satisfaction.

Key Takeaways

By following these email A/B testing best practices, you will position yourself best to achieve success. Testing should be a mandatory part of your email process if it isn't already. Remember that testing is only worthwhile if you act upon your findings. Use it as an opportunity to give your audience what they want!

  • Don’t just test once and forget. Develop a culture of continuous optimization.
  • Spend time understanding your findings so that you can better understand your audience.
  • Only ever change one variable at a time when A/B testing.

Completing email A/B testing manually is a laborious process. Wouldn’t it be great if an email tool could handle it for you? That’s just part of what Instantly offers. The best part? You can get started today.

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