What does ‘email A/B testing’ mean?

What is an email A/B test?

An email A/B test is a method whereby you send two different versions of the same email to small groups of recipients to see which version yields the best results. The aim is to make decisions based on data rather than gut feeling.

These two versions are typically referred to as version A and version B. They might, for example, be two different subject lines, two variations of a call to action, or two different send times.

Once the test is complete, analyse the results and use the winning version in future campaigns, or send the best version to the rest of your mailing list.

Email A/B testing is particularly common in email marketing, where even small improvements can have a significant impact on open rates, click-through rates, conversions and revenue. That is why A/B testing is an important tool for small businesses, online shops, SaaS companies and larger marketing teams alike.

Why is email A/B testing important?

Many companies send out newsletters and promotional emails without really knowing what works best. They choose a subject line, a design or a message based on experience or personal taste, but this doesn’t always yield the best results.

With an email A/B test, you can determine which version performs best among your recipients. This makes your email strategy more targeted and effective.

This is particularly important because recipients’ behaviour changes over time. What worked last month won’t necessarily work in the next campaign. Testing helps you to adapt your communication on an ongoing basis.

• You’ll gain a better understanding of what your target audience responds to
• You can improve open rates and click-through rates
• You reduce the risk of running ineffective campaigns
• You’ll lay a better foundation for conversions
• You’ll take a more data-driven approach to email marketing

In practice, this means you can get more value out of the same mailing list. Instead of simply sending more emails, you can improve the emails you already send.

How does an email A/B test work?

In a classic email A/B test, you select a single element that you want to test. You then create two versions of the email, with only that one element differing between them.

The two versions are sent to different segments of the target audience. After a set period, the results are analysed, and the version that performs best against the chosen metric is declared the winner.

For example, if you want to test a subject line, the rest of the email should remain the same. Otherwise, it will be difficult to tell whether the difference in results is due to the subject line or something else in the content.

• Choose a clear objective for the test
• Test only one variable at a time
• Divide the recipients randomly into two groups
• Send version A to one group and version B to the other
• Assess the results using the same criteria
• Use the winner as a learning point for the next broadcast

Most email platforms have built-in A/B testing features. This makes the process straightforward, but it is still important to plan the test properly if you want to be able to rely on the results.

What is the difference between A/B testing and standard optimisation?

Standard optimisation might involve changing a subject line because you think it will be more effective. An A/B test goes one step further by comparing two versions under identical conditions.

This means that you don’t just tweak your email, but actually document the impact of the change. This makes your conclusions more reliable and useful in the long term.

What can you test in an email?

There are many options when it comes to A/B testing emails. Some elements have a particular impact on whether the recipient opens the email, whilst others are most important for clicks and conversions.

Elements that are frequently tested

• Subject line
• Preheader text
• Sender's name
• Broadcast time
• Email subject line
• Images versus more text
• Placement of the call to action
• Colour and text on buttons
• Length of the content
• Offer, discount or message

The subject line is one of the most thoroughly tested elements, as it has a direct impact on whether the email is opened. Even small changes in wording, length or tone can make a noticeable difference.

Calls to action are another obvious area to focus on. Should the button say “Read more”, “View offer” or “Buy now”? An A/B test can reveal which wording encourages the most recipients to click.

You can also test more strategic aspects such as segmentation, personalisation or the type of offer. In this case, the test often becomes more advanced, but also more valuable, as it reveals what actually motivates the recipient.

The key metrics in an email A/B test

A test only delivers business value if you’re measuring the right things. That’s why you should choose your key KPI before launching the test.

The best metric depends on the purpose of the email. If the goal is to increase the number of opens, it makes sense to focus on the open rate. If the goal is sales, clicks and conversions are more important.

• Opening rate: How many people open the email
• Click-through rate: How many people click on links or buttons
• Conversion rate: How many people carry out the desired action
• Turnover: How much revenue the email generates
• Churn rate: How many people choose to cancel their subscription?
• Bounce rate: How many emails are not delivered

It is important not to look at a single figure in isolation. For example, one version might generate more page views but fewer clicks. You should therefore evaluate the test based on the metric that is most relevant to the campaign.

In some cases, it makes sense to have both a primary and a secondary objective. This can provide a more nuanced picture of how the two versions actually perform.

Examples of email A/B testing in practice

It may be easier to understand the value of an email A/B test through specific examples. Here are some typical situations in which companies use this method.

Test of subject line

An online shop is going to send out a newsletter featuring weekend offers. Version A has the subject line “Weekend offers: Save 25% today”, whilst version B is titled “Weekend only: 25% off selected items”.

Both emails have the same content, but the subject line that generates the most opens wins the test.

Testing the call to action

A company wants to attract more registrations for a webinar. Version A says “Register here”, whilst version B uses “Book your place”.

If version B generates more sign-ups, the company can use that wording in future campaigns.

Testing the broadcast time

A B2B company is unsure whether its target audience responds best to emails sent on Tuesday morning or Thursday afternoon. By testing these two times, they can get a clearer picture of when recipients are most active.

This kind of insight can significantly improve results over time, especially if the company sends emails on a regular basis.

The benefits of using A/B testing systematically

When A/B testing becomes an integral part of your email marketing, you gradually build up a better understanding of what your target audience prefers. This leads to better decisions and makes your marketing efforts more effective.

The benefit isn’t just better results for individual campaigns. The greatest benefit often lies in the ongoing learning that can be applied across newsletters, automated workflows and promotional emails.

• You minimise guesswork in your communication
• You’ll get to know your target audience better
• You'll improve your performance over time
• You can demonstrate the impact of changes
• You’ll get more value out of your existing traffic and leads

For businesses with a high volume of campaigns in particular, small improvements can quickly add up to significant results. A higher click-through rate or conversion rate across numerous campaigns can have a major financial impact.

Common mistakes in email A/B testing

Although A/B testing is a powerful tool, many people use it incorrectly. This can lead to misleading results and poor decisions.

• Several elements are tested at the same time
• The test group is too small
• The purpose of the test is unclear
• It is too early to assess the outcome
• The winner is chosen based on the wrong measurement point
• The lessons learnt are not being applied in subsequent campaigns

If you change the subject line, design and call to action all at once, you won’t know what actually made the difference. That’s why it’s usually best to keep the test simple.

Another common mistake is to stop the test too soon. Some recipients open and click straight away, whilst others respond later. If you draw conclusions too early, you may end up choosing the wrong version.

How to avoid the most common mistakes

• Define one clear test objective at a time
• Use your target audiences and your broadcasting conditions
• Let the test run long enough to collect data
• Record the results after each test
• Turn the results into concrete improvements

Email A/B testing in relation to SEO and digital marketing

Although email A/B testing is not SEO in the traditional sense, it is closely linked to the overall digital marketing strategy. Email can drive traffic to landing pages, blog posts, product pages and campaign pages, all of which also play a role in online visibility and conversion.

By testing your emails and improving your click-through rate, you’ll drive more targeted traffic to your website. If recipients land on relevant pages with high-quality content, this can enhance the overall customer journey from initial contact to purchase.

A/B testing in email marketing should therefore be seen as part of a wider optimisation process. It is not just about getting opens, but about creating a better connection between the message, the landing page, the user experience and conversion.

When does A/B testing for emails make the most sense?

Email A/B testing is particularly useful if you send out a lot of campaigns, have a sufficiently large mailing list, or are actively involved in performance marketing. The more data you have, the easier it is to identify clear differences between the versions.

However, this does not mean that smaller businesses cannot use this method. Even with a smaller list, A/B testing can be valuable if you take a structured approach and test the most important elements first.

• When you want to improve the open rate of your newsletters
• When you want to boost sales from promotional emails
• When you want to optimise automated workflows
• When you want to find out more about your audience’s preferences
• When you want to take a more data-driven approach to email marketing

If you only have a few episodes and a very short playlist, the results may be harder to interpret. But even in this case, simple tests can still provide useful insights, especially if they are repeated over time.

How to get started with email A/B testing

If you want to start using A/B testing for emails, it’s a good idea to keep it simple. Choose one element that’s likely to make a big difference, and build up your experience gradually from there.

• Start by testing subject lines
• Define one clear criterion for success
• Use your email platform to segment recipients automatically
• Compare the results objectively
• Save your insights in a permanent test archive
• Repeat the process continuously

Over time, you can test more advanced features such as personalisation, targeted offers or content structure. The most important thing is to make testing a regular habit rather than a one-off exercise.

In this way, email A/B testing becomes not just a technical tool, but a key part of your strategy for improving your email marketing.

Conclusion: What is an email A/B test?

An email A/B test involves comparing two versions of an email to find out which one performs best. It is a practical, data-driven method for improving your email campaigns and achieving better results.

This method is used to test everything from subject lines and calls to action to send times and content. When carried out correctly, it provides valuable insights into what your target audience responds to.

For businesses that take email marketing seriously, A/B testing is one of the most effective tools for ongoing optimisation. It makes communication more effective, improves results and leads to better-informed decisions.

In short, email A/B testing is a way to send smarter emails, learn faster and get more out of every single email.