Email A/B Testing: Must-know Basics!

Written by: Chris Donald

Published on: 08-02-2023

Chris is Managing Partner at InboxArmy and has more than 25 years of experience in email marketing

It’s likely that terms like A/B Testing can sound confusing and daunting, especially if you’re just starting with email marketing. Nonetheless, email A/B testing is an incredibly useful tool for email marketers who want to maximize the effectiveness of their email campaigns.

In fact, A/B testing is a common practice in the web space, with many businesses leveraging A/B testing for various aspects of their sites and email campaigns.

Simply put, email A/B testing is not a particularly difficult concept to understand, so don’t let it scare you off!

In this guide, we’ll cover the basics of email A/B testing for email marketers. Then, we’ll look at what email A/B testing is, how it works and why email marketers should be utilizing email A/B testing to optimize their email campaigns.

What Is A/B Testing In Email Marketing

Email A/B testing – also called email split testing – involves sending two different versions of an email to two randomly segmented halves within the same email list. This helps to measure how one change impacts the outcome of the marketing campaign.

Typically the changes are usually implemented in the subject line. Nonetheless, the changes may also be incorporated into the email body. Eventually, the email that gets the most opens and clicks is considered the better, more effective version and sent to the remaining subscribers.

Significance of Email A/B Testing For Marketers

Significance of Email AB Testing for Marketers

In general, A/B split testing enables evaluating and comparing two versions of content to see which version performs best. However, many brands and marketers overlook email A/B testing and its ability to maximize email performance. This is a big mistake. The truth is email A/B testing is integral for email marketing.

Here are just a few reasons email A/B testing is essential for email marketers:

1) Enables Identification of Specific Improvements:

To begin with, if you keep changing different elements of email content, it might be challenging to track which email element had the most positive impact.

Likewise, even if you change an element but don’t track the email performance, you won’t be able to identify which email elements are working best. With email A/B testing, you can measure email performance after each test and determine the best email content elements.

2) Facilitates Improved Open Rates:

A well-crafted email subject line can make all the difference in email open rates. With email A/B testing, you can create two email subject lines, preview texts, etc., to experiment with which one yields the higher open rate. This helps enhance open rates as email recipients are more likely to open emails if they find the email subject line meaningful and engaging.

3) Promotes Click-Throughs:

Email A/B testing helps track which email version yields the most clicks. It enables email marketers to understand what email elements, such as CTA (Call To Action) buttons, are working and not working. This way, email marketers can better understand which content and links subscribers tend to click on.

For example, if you split test two emails with different CTA’s and find one which has a higher email click through rate, then you can use this email as a template for future emails and optimize it further.

4) Improved Conversion Rates And Sales:

Email A/B testing helps email marketers optimize their email campaigns. This allows marketers to make better strategic decisions. In addition, since email messages are more effective and relevant, they tend to have more favourable outcomes, leading to more conversions and revenue.

Overall, email A/B testing plays an important role in helping email marketers test and optimize their campaigns. By honing the right elements of their email campaigns, they can maximize open rates, click-throughs, and conversions.

Should you Test Your Whole List Or Just A Part Of It?

A prominent question email marketers have is whether they should test email campaigns with their entire email list or just a part of it.

In most cases, the answer is that it’s advisable to test your entire list. This helps you get a clear idea about how email campaigns would actually perform if they were sent to all your subscribers. In this way, you can manage email campaigns more effectively, as you know how a larger group of recipients would react to them.

At the same time, there are a few scenarios where you might not require to test your entire list. So here’s a quick rundown on when email A/B testing with a part of your list is most beneficial:

You’re introducing a limited-time offer: When you’re looking to get as many conversions as possible, it’s advisable to test a few hundred recipients and then send out the better version to your entire list.

Your list is extensive: When you’re being charged per email address and have a comprehensive list, email A/B testing with your entire email list can be pretty costly. Even then, test the most significant possible sample you can afford. 

Further, ensure that the ids selected are chosen randomly for accurate results. This will help you better understand your email campaign’s performance without breaking the bank.

You are experimenting with a completely new or unique idea: If you’re trying something unique, it may help to be cautious about how many customers can see it. This precautionary measure is more to ensure that you’re not risking too much with something completely new.

Nonetheless, show at least a few hundred people a version of each of your email A/B tests. If your list is extensive, you can also try randomly selecting a couple of thousand people to understand better how your email campaign would perform.

In sum, with email A/B testing, the bigger your test sample, the more reliable the results will be. 

Furthermore, since your objective is to collate empirical data and assess which version of your A/B test material works better than the other, it is essential to implement random splitting. Avoid deliberate selection of recipients or even using two lists from different sources. These could affect the accuracy of your results.

A/B Testing Email Examples: What You Can A/B Test In Emails

AB Testing Email Examples What You Can AB Test In Emails

You can A/B test any element of email that you think can have an impact on user engagement. Here are some examples:

1) Subject line:

A clear email subject line can hit all the right notes and get more recipients to open your email. For this reason, A/B testing subject lines can help you optimize your emails.

While some industry sources recommend around 40 characters as the length of subject lines since it’s smartphone-friendly, some recommend subject lines to have between 9 to 60 characters.

Nonetheless, it’s not just the character count but also the behavior and mindsets of contacts in the specific list which may vary.

For example, you could run A/B testing for the following factors:

  • Length: A 40-character subject line versus another having 55 characters.
  • Numbers: Try a subject line with numbers versus one without, i.e., ‘5 Tips to Improve Your Email Open Rates’ vs. ‘Tips to Improve Your Email Open Rates.’
  • Punctuations: You could try a subject line with punctuation versus one without. For example, ‘You Won’t Believe What Happened!’ vs. ‘You Will Not Believe What Happened.’
  • Company/Team-member name: You could include your company name/team member’s name in one option versus no personalization. For example, ‘Here’s how XYZ Ltd Can Optimize Your Open Rates’ vs. ‘Here’s How You Can Optimize Your Open Rates.’
  • Symbols/Emojis: Try an email subject line with a symbol or emoji versus one without. For example, ‘It’s Time to 🎉Celebrate the Holiday Season!’ vs. ‘It’s Time to Celebrate the Holiday Season!’
  • Capitalization: Test the subject lines with all capital letters versus ones with standard sentence case. For example, ‘Grab Xyz’s Latest Offer Now’ vs. ‘grab xyz’s latest offer now.’

Other comparative tests you can run for the subject line include:

  • Brief vs. Descriptive: ‘Signup Now!’ vs. ‘Signup now and get a 10% discount.’
  • Question vs. Answer: ‘Wondering why email marketing works better?’ vs. ‘Email marketing works better than other channels.’
  • Relaxed vs. Urgent: ‘Save up to 50 % Now!’ vs. ‘Last Chance to Buy Before Price Increase!’
  • Positive vs. Negative: For example, ‘Save more money at our store vs. ‘Don’t miss this opportunity to save.’

2) Personalization:

Studies indicate that personalization increases open email rates by 29%. You can run A/B testing using email marketing personalization, such as using the sender or subscriber’s name in the email subject line or body. The tests will help you understand which email personalization works best for your email and audience. You can also compare how email personalization options, such as open and click-through rates, affect email engagement metrics.

Although personalization is a valuable strategy, it should not be overused. Moreover, if your subscribers see their names appearing in your emails very often, it may lose its effectiveness.

For instance, you can personalize emails with:

  • the customer’s name, location, company size, or position in the company.
  • the customer’s previous purchases or interests.
  • the customer segment they belong to.

3) Images:

Images are an effective tool to motivate your customers to act in the desired way. A/B testing for images is an interesting way to understand how your readers respond to different images and their effectiveness in facilitating engagement. 

Our top-of-the-mind ideas of images to test include the following: 

  • Image of persons versus product images
  • One versus several images
  • Text versus no text on images
  • Video screenshot 
  • CTA in the image versus CTA away from the image
  • Static image versus animated GIFs 
  • Serious versus light-hearted images
  • Colorful versus B&W visuals
  • Stock image versus the image of your employee/customer using the product

More significantly, regardless of your approach when A/B testing images, ensure that you use JPG, GIF, or any other common file type. This will maximize the chances of the pictures reaching your target inboxes.

4) Email design:

As per findings, your marketing email typically takes around 3 seconds to get your reader’s attention. For this reason, it’s time to double down and optimize your email strategy.

Implementing an email design that appeals to their eye is one of the most successful email A/B tests. Furthermore, you need to ensure that your design is mobile-friendly, too. In this scenario, testing responsive design is of critical importance.

For example, two emails may likely throw up different results based on what you’re testing for. A plain-text version may have a better open rate. However, when it comes to potential customers clicking, a design template that contains a video as a GIF may attract more people to click and therefore is more effective.

For starters, A/B testing of larger text and more evident CTAs can help email marketers identify and find the more effective design.

5) Email layout:

Generally, email A/B tests look at email layouts and identify the email with higher open and click-through rates. This is further based on email design elements such as email length, the number of email images, the email’s CTA button, and email text placement. All these elements are crucial in determining email effectiveness.

For instance, test whether emailers with two or three columns get more clicks.

For instance, A/B test whether:

  • emailers with two or three columns get more clicks than emails with one column.
  • determine if full-width images generate more clicks than smaller images in the email layout.
  • the placement of CTA buttons affects open rates and click-throughs.
  • readers respond more to the CTA button placed at the top of the email or if it’s more effective when it’s in the middle or at the end of the email.

Additionally, you can also test the number of words in the email body to determine which is more effective. For instance, if a longer email generates more interest, it could be because readers are getting more information or because they find the emails more interesting.

6) Preview text:

This refers to the text snippet that email recipients see after the email subject line. Often, the message preview element gets overlooked when testing email campaigns. Also known as email pre-headers, preview text can be customized using email marketing tools in most cases.

A/B testing may be slow-moving and tedious if you manually test it. But rest, but rest assured, it’s worth it in the end. After all, most of us have, at some time or another, opened an email only after being intrigued by the email’s preview text.

You can test the following variations:

  • Email first line: You can copy the email’s opening line and use it as preview text. For example, “Hey there, our season’s-end sales are here with exciting offers!” 
  • Short summary: For emailers with a lengthy body, you can write a brief overview of the email content in the email preview text. For example: “Enjoy up to 50% off on branded products. Explore the offers now!”
  • Call to Action: Email previews can also contain email CTAs.For example, “Explore amazing offers. Click now!”

7) Headline text:

If your email contains a headline, A/B testing is a must. After all, email headlines are the first thing readers see and help you determine whether they should keep reading. The tests can be similar to a subject line and can be used to optimize email designs. In addition, email marketers can test different fonts, sizes, and colors of the headlines to discover what works best.

Also, they can conduct the following email headline A/B tests to determine the best-performing option:

  • If changing the order of words in the headline leads to more clicks or an increased open rate.
  • If using a question headline works better than a straightforward one.
  • If using uppercase letters instead of lowercase makes an impact.
  • If certain words in the headline evoke more emotions and lead to better engagement.
  • If headlines that are humorous or witty get higher attention.

8) Call To Action:

This is one of the most critical and fundamental email elements to test. Not only is it crucial for garnering clicks, but it’s also the final step in email conversion.

Testing the following CTA features can help you optimize your email marketing:

  • CTA repetitions: Since too many links can overwhelm or confuse customers, ideally, have just 2 -3 links pointing to the same objective. This will help drive conversions rather than drop-offs.

Notably, CTAs should be placed on a clickable button. Another handy hint for you to consider is that incorporating a CTA in your sign-off or postscript (P.S.) can be effective.

  • Text on buttons: Test both short and long text versions on CTA buttons. Alternatively, you can experiment with conventional CTA versus a more edgy, creative one.

Likewise, make the most of your A/B testing to see how much you can push the envelope. Experiment with the tone and style of text, size, fonts, and all capitalizations, to know which word or phrase and style works best and facilitate a more excellent conversion.

For example, the more traditional CTA, ‘Learn More’ or ‘Sign Up’ versus a more creative version like, ‘Be Part of this’ or ‘Get Started Now.’

Noteworthily, buttons with all caps have been observed to perform the best. So you could give it a try too!

  • Different colored buttons: Using contrasting colors can increase the visibility of your email’s CTA. A/B testing colored buttons can be helpful in email campaigns by allowing email marketers to determine the best contrast and color of the CTA button.
  • For example, some marketers feel that the color red helps boost the click-through rate. At the same time, pay attention to how the color in your email ties in with your marketing campaign.
  • CTA button location: A/B testing responses to varying the location of your CTA button can often produce significant changes in email click-through rates.

For example, placing the CTA at the bottom of the email, or towards the middle or even above the fold, can get readers to see it easily without having to scroll and facilitate engagement.

Making some CTAs more visible and accessible than others can make a significant impact.

  • Arrows and other visual elements: You can guide your reader by providing a sense of direction with visual cues to essential details on the pages of your email campaigns.

Testing visual elements such as arrows or eye-catching images help email marketers understand how to better optimize email design for improved email conversions. In addition, it helps in organizing the information and creating a flow.

9) Different Testimonials:

Including client testimonials in your email can improve conversion rates by assuring your users of your brand. For example, you can run A/B tests containing two testimonial versions – one having a short, simple, and convincing customer story or an email with a longer and more detailed review. This will help you determine which email works best.

Another tactic is to include the customer’s name and company logo in the testimonial. This gives a sense of credibility, prompting customers to feel more connected and confident towards your brand.

Testing the placement of customer testimonials can also be effective. Experiment with positioning them at the top, bottom, or within the body of the email to see which version garners better engagement.

10) Links And Buttons:

By testing the links in email campaigns, email marketers can gain actionable insights into how their email recipients are behaving. From the type of link they’re clicking to the location of their click, email marketers can get a better idea of how receptive email recipients are to their email campaigns.

For example, links like read more, shop now, download here, etc., can help email marketers understand what email recipients prefer.

Testing the size, color, and shape of buttons can also help email marketers gain insights into user behavior. Bigger buttons have been found to prompt more clicks, while the shape and contrast of the button can also make a difference. Even testing the location of your links and buttons can lead to surprising results.

Testing these elements is essential to understanding the best way to create compelling emails that inspire action.

11) Copywriting:

A/B testing the length, word order, and tone of your email marketing helps you understand what messaging triggers the desired engagement. While the favorite advice of most industry experts is to write short sentences (no longer than two lines) with CTAs being the shortest line, you may want to implement email A/B testing to find the best email copy for your list.

Moreover, email A/B testing can help you identify which email’s email copy resonates best with your target audience: Shorter or longer, bullet points or numbered, Q&A format, formal or informal, order of content, and so on.

12) Closing Text:

Every email must have a closing statement to wrap up the email. This often contains a call-to-action to encourage readers to do something, such as taking a survey or visiting your store.

A/B testing can help email marketers, for example, compare two versions of email closing statements, with and without call-to-actions, two different phrasings, signatures, or even email footers.

Examples of closing statements that work well include:

  • We look forward to hearing from you soon.
  • Don’t forget to complete the survey by clicking here.
  • We know you’ll love our products, so come check us out now!
  • Thanks for being part of our community.
  • Let us know if you need more help.

13) Offers Types:

Depending on the circumstances, you may want to test which kind of offer appeals to your email recipients. For instance, if you’re sending promotional offers for a product or service, deals or discounts, free shipping, or other such incentives to shop with you, you can use email A/B testing to see which offer type works best.

Furthermore, how you present your offer to recipients can also be optimized using email A/B testing. For instance, the fear of loss can be more compelling than the desire to gain. Accordingly, you should present your offer in a way that highlights what they stand to lose if they don’t take advantage of your offer.

Phrases like “Last chance” or “Hurry, limited time offer” may help email marketers garner higher email open rates.

Keep in mind that the most successful email campaigns involve a combination of the above tests. Therefore, it is important to use each email A/B testing method in your strategy to identify the most effective design. This way, you can create emails that will drive more conversions and boost user engagement.

How To Set up An Email A/B Test?

How To Set up An Email AB Test

Setting up an email A/B test is a straightforward process. Here are the steps for setting up an email A/B test:

1) Identify your objective:

Firstly, decide which email elements you want to compare and improve.

Further, when implementing email A/B testing, to improve metrics like open rates, try to measure the outcomes more holistically. This means assessing how conversion rates vary from the different emails. Similarly, since subject lines set the expectations about the content, look for how they influence email engagement and clicks.

2) Choose the variable:

Once you’ve decided on the objective, identify the email elements that will be tested, then develop multiple versions. Test only one variable at a time because if there are considerable differences between control and variable emails, you’ll be unable to determine which email element contributed to the email engagement. 

Testing individual elements in an email A/B test may be tedious, but it will facilitate more informed conclusions.

3) Establish parameters:

This step involves finalizing aspects that ensure the tests proceed smoothly. The parameters include the following:

  • Duration: Typically, you’ll have to wait at least a day before the results trickle in.
  • Recipients: When A/B testing within a specific segment, it is advisable to have a significant audience size for the results to be statistically reliable.
  • Testing split: Once the segments to receive the test are decided on, you’ll need to split the send. For example, you could send a 50-control version and 50-variable version split, or send control version X to 20%, test version Y to another 20%, and finally, the winner to the remaining 60%.
  • Metrics being measured: Identify the metrics you want and how to obtain the data before testing. 
  • Other variables: Factor in variables like holidays, which are not in your control but could impact the final test results.

4) Implement the test:

You can run the email A/B testing in two main ways outlined below:

  • Automatic: Having your ESP manage the split-sending is a convenient and recommended option for simple tests that are primarily driven by surface-level goals such as increasing open rates.
  • Manual: You can create two separate emails and manually send them. While it is more intensive, this method is advisable if you want data insights like website engagement, which are more granular and in-depth than your ESP.

5) Evaluate the results:

If you’ve planned well and were clear about your objectives, you’ll know exactly where to look once the test is completed. At this stage, you can compare the results. 

If you need a re-test to confirm the first results, follow the process with the same cohort to check if the results are authentic. Once you finish the process, you can share your findings with your team.

Frequently Asked Questions (FAQs)

Q1. What is Email A/B Testing?

Email A/B testing refers to the process of sending one version of your campaign to a specific group of your subscribers and a different variation to another group of subscribers. The ultimate goal is to identify which variation of your email campaign achieves the best results.

Q2. How many emails can you send to execute the A/B test?

You can typically send two different variations of your email to 2 different sample groups of your email list for the purpose of email A/B testing. However, the sample size of each group should be large enough to obtain statistically significant results. Otherwise, you might end up with a false conclusion.

Q3. What should I A/B test in an email?

You can run A/B tests for several email elements to see what resonates best with your readers. Some commonly tested components include – email subject lines, email sender names, email content/copy, preview text, HTML vs. plain text, email length, personalization, CTAs, design, layout, and imagery.

Q4. How long should you run an A/B email test?

Running an email A/B test for at least seven days is advisable to attain statistical significance. But ideally, aim for 1-2 weeks. If, for some reason, you can’t run a test for an entire week, then try to go for the most extended duration you can manage. If unsure about the results, rerun the test for at least seven days.

Q5. How many users do you need for email A/B testing?

The bigger the test sample, the more reliable your results will be. However, to run an email A/B test of a sample of your list, you should have a decently large list size comprising at least 1,000 contacts.

If you have fewer users in your list, then the proportion of users you need to A/B test to obtain significant results gets bigger.

Q6. When should you stop an A/B test?

It’s a good idea to continue your email A/B testing until you reach 95-99% statistical significance. This means that you should have enough data to prove that the results are consistent and that there is a low chance of random variation.

Once you reach this degree of statistical significance, you can analyze the results and determine which version was more successful.

You may also want to consider other factors, such as your current goals, budget constraints, and your resources. This can help you decide when to terminate the test or whether to rerun it for more accuracy.

Q7. How do you measure the success of an A/B email test?

It’s critical to know how to measure whether or not your A/B email tests are working. When you’re testing, based on your business objectives, the three primary metrics to follow are open rate, click rate, and conversion rate.

Notably, the variables being tested should correspond to at least one of these metrics that directly or indirectly help improve sales.

For instance, if your objective is increasing eyeballs for your brand, optimize for open rate; for more visitors to your website, test for the click rate; focus on conversion rate if your goal is to boost revenues.

Q8. Can you run multiple email A/B tests at the same time?

Running A/B tests on multiple email components simultaneously often leads to interferences that result in choosing an inferior combination of variants. 

Therefore, while you can test more than one variable for an email, just try each one at a time. Otherwise, you will be unable to determine which variable was responsible for the observed response difference.

You can, however, test multiple variables simultaneously if there is no correlation between them. For example, you can run an A/B test on different email subject lines and personalization strategies.

Just make sure that the two components you are testing are independent of each other.


Email A/B testing is essential to optimize your email campaigns for maximum success. It helps determine which email strategies or elements work best and drives the most conversions.

At the same time, email A/B testing should not be considered daunting and intimidating. With some planning, strategizing, and patience, you can quickly identify email elements and strategies that work best for your email campaigns. Then, with the proper testing approach, you can ensure your email campaigns reach their maximum potential. Also, if you are looking for someone to work on your email campaigns then feel free to contact us, we are an experienced email agency and we support 50+ ESPs.

About Author

Chris sent his first email campaign in 1995. He’s worked directly with Fortune 500 companies, retail giants, nonprofits, SMBs and government agencies in all facets of their email marketing and marketing automation programs. He’s also a BIG baseball fan, loves a good steak, and is mildly obsessed with zombie movies. For more information follow him on linkedin

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