What Is A/B Testing In Email Marketing And How Do You Do It

There are very few marketing tactics that allow you to make genuinely data-driven decisions with as much clarity and confidence as A/B testing in email marketing. For businesses that are serious about improving the performance of their email list and getting more out of every campaign they send, understanding what A/B testing is and how to do it properly is not optional, it is essential. Whether you are a seasoned email marketer or someone just getting started, split testing gives you a structured, reliable way to learn what your audience actually responds to, rather than what you assume they will.

So, what is A/B testing in email marketing, and how do you go about doing it in a way that produces meaningful results? Let us break it down properly.

What Is A/B Testing In Email Marketing?

A/B testing, also commonly referred to as split testing, is the process of sending two versions of the same email to different segments of your email list to determine which version performs better. You change one variable between the two versions, send each version to a portion of your audience, and then measure the results to see which one wins. The winning version can then be sent to the remainder of your list, or simply used to inform how you approach future campaigns.

The concept is straightforward, but the value it delivers is significant. Rather than relying on gut instinct or guesswork, you are letting your actual subscribers tell you what works. Over time, this builds a compounding understanding of your audience that no amount of industry advice can replicate, because your audience is unique to your business.

Platforms like Mailchimp and Klaviyo have built-in A/B testing functionality that makes this process accessible even for smaller businesses without dedicated marketing teams.

Why Split Testing Your Emails Matters

Email marketing remains one of the highest-returning channels available to businesses of all sizes. But sending emails without testing them is a bit like cooking a new dish and never tasting it as you go. You might get lucky, but you are far more likely to miss the mark without some form of ongoing refinement.

When you commit to regular split testing, you start to build a picture of the preferences, behaviours and motivations of your subscribers. You learn whether your audience responds better to personalised subject lines or direct ones, whether long-form emails outperform short ones, and whether a single call to action drives more clicks than giving subscribers multiple options. These are insights that genuinely move the needle on your email marketing performance over time.

It also reduces the risk that comes with making large-scale changes to your email strategy. Instead of rolling out a completely new approach to your entire list and hoping for the best, you test it first, learn from the results, and then make informed decisions based on real data.

What Can You Test In An Email Campaign?

One of the most important rules of effective A/B testing is that you only change one variable at a time. If you alter the subject line, the sender name, the call-to-action button and the email layout all at once, you will have no way of knowing which change was responsible for any improvement or decline in performance. Focus matters here.

Here are some of the most commonly tested variables in email marketing:

• Subject lines: This is arguably the most impactful element to test, as it directly influences whether your email gets opened in the first place. You might test a curiosity-driven subject line against a straightforward benefit-led one, or experiment with personalisation by including the recipient's first name.

  Preview text: The short snippet of text that appears alongside the subject line in most email clients. Changing this can have a meaningful impact on open rates.

  Sender name: Some audiences respond better to emails that come from a person's name rather than a brand name. Testing this can reveal a lot about how your subscribers prefer to receive communication.

  Call to action: The wording, colour, size and placement of your call-to-action button or link can all influence click-through rates. Testing a button that says "Shop Now" against one that says "See What's New" is a simple but often revealing test.

  Email layout and design: A single-column layout versus a multi-column one, plain text versus HTML, or image-heavy versus text-heavy formats are all worth testing depending on your audience.

  Send time and day: When you send your emails can be just as important as what is inside them. Testing morning sends against afternoon sends, or weekday sends against weekend ones, can surface patterns that are specific to your subscribers.

  Email length and content depth: Some audiences want a concise message with a single clear action. Others prefer more context and detail before they are ready to engage. Testing both approaches helps you understand where your subscribers sit.

  How To Set Up An A/B Test In Email Marketing

  Setting up a split test does not need to be complicated, but it does need to be done with some care to ensure the results you gather are actually meaningful and actionable.

  Define What You Want To Learn

  Before you create your two email versions, be clear about what question you are trying to answer. Are you trying to improve your open rate? Then test your subject lines. Are you trying to increase clicks? Then your call to action or email body content is the right place to focus. Every test should start with a clear hypothesis.

  Segment Your Email List Correctly

  For a test to be valid, the two groups of subscribers receiving your emails need to be as similar as possible. Most reputable email marketing platforms will handle this automatically when you set up a split test, randomly assigning subscribers to each version. If you are doing this manually, make sure you are not inadvertently sending one version to your most engaged subscribers and the other to those who rarely open your emails, as this will skew your results significantly.

  Choose A Meaningful Sample Size

  Testing your two versions on just a handful of subscribers will not give you reliable data. The larger your test group, the more confidence you can have in the results. As a general principle, the bigger your email list, the more meaningful your test results will be. If you have a smaller list, be cautious about drawing firm conclusions from a single test. Look for patterns across multiple tests over time.

  Measure The Right Metrics

  Decide before you launch which metric you are using to determine the winner. Open rate, click-through rate, conversion rate and revenue generated are all valid metrics depending on what you are testing. Changing your success metric halfway through a test undermines the integrity of the results. Stick to the one that aligns with the goal you set at the beginning.

  Give The Test Enough Time

  Most email tests produce the bulk of their data within the first 24 to 48 hours after sending, but resist the urge to call a winner too early. Let the test run its course before making any decisions, and make sure you are accounting for different subscriber behaviour across different times of day.

  Building A Culture Of Continuous Testing

  The businesses that get the most out of their email marketing are not the ones that run a single split test and declare the work done. They are the ones that treat A/B testing as an ongoing practice, something baked into every campaign they send. Each test generates an insight, and each insight informs the next campaign. Over time, this creates a compounding advantage that is genuinely difficult for competitors to replicate.

  Keep a record of every test you run, what you tested, what the results were, and what you decided to do as a result. This becomes an invaluable reference document that helps you avoid repeating tests unnecessarily and ensures your strategy is always moving forward based on evidence rather than assumption.

  Getting Started With Email A/B Testing

  If you are not already running split tests on your email campaigns, the good news is that starting is straightforward. Pick one element of your next email, form a clear hypothesis about what you expect to happen, set up the test using your email platform, and let the data do the talking. You do not need a large budget or a specialist team to begin, just a commitment to learning from your audience and a willingness to let the results guide your decisions.

  A/B testing in email marketing is one of the most reliable ways to improve your results steadily and sustainably. It removes the guesswork, builds your understanding of your subscribers, and ultimately helps you create emails that genuinely resonate with the people on your list. Start small, stay consistent, and the insights will follow.