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A Guide to Email Testing

Oct 5, 2022

Email is still one of the easiest and fastest ways to get in front of your audience. Because of this, today, all our inboxes tend to be flooded with notifications, newsletters and more.

If you’re running a business or overseeing an email marketing campaign for your clients, your messages need to stand out from the rest to improve user engagement and boost conversions.

This is where email testing comes into play. Instead of relying on hunches or assumptions to make your vital email marketing decisions, split testing provides you with the proof you need that one approach is going to get you better results than another. With email testing, you will take two versions of an email and send them to two groups within your user pool. Whichever version performs best, whether that looks like more opens, click-throughs, or even conversions, is the one to send to everyone else.

Split testing for email is one of the best ways to ensure that your email marketing campaigns are set up to encourage your audience to take more action, like signing up for a service or making a purchase. Keep reading to find out more about email split testing.

What is Email Testing?

At some point, most of us likely received an email that was interesting enough for us to open it. Maybe it was the subject line that sparked your interest, or there was an offer inside that was simply too good to refuse. Either way, there would have been something about that email that got you to click on it, read it, and follow a call to action.

Chances are, that email went through a process of split testing or A/B testing before it reached your inbox. This process involves sending two versions of the same email to different groups, with variations that might include small changes like differences in image placement or wording or more significant changes such as differences in formatting. The differences will usually depend on what you are trying to get your subscribers to do when they read the email.

For example, if you want to find out which version of your email will get the most open rates, then you might change the wording of your subject line to include a question or to be funnier than the other. If increasing click-throughs is your main goal, then you might test differences in the call-to-action button in the body of your email to see which one performs best.

No matter your goal with your email marketing, two versions of an email will be sent to a small pool of users. The version that gets the most click-throughs, opens or conversions is the best one to send to all your other subscribers.

Why is Email Testing Necessary?

Split testing for emails is a very effective way of finding out what works well and what doesn’t get great results in your email marketing without the risk of throwing away your entire campaign. Rather than simply assuming that your customers are going to prefer one version of an email over another, you can run an A/B test to find out for definite. The more split tests you run, the more information you will be able to gather and use when sending future emails. Regular A/B testing is one of the most effective ways to help you build a successful email marketing strategy over time.

Email Testing Goals

Like anything in digital marketing, it’s crucial to have a clear goal and objective when testing emails. Of course, you can get valuable results from running a quick A/B test, but you will get access to more powerful data when you employ a more precise testing strategy for your emails.

Split testing for emails can be used anytime, but it can be beneficial when you want to gain insights into a specific email format or a new campaign. Before starting A/B testing, the first step is establishing what you are testing and why. At this stage, you may want to ask a few questions, such as why you are testing a particular variable, what you want to learn from it, and the impact that the specific variable has on the performance of the email.

Tools You Can Use

There are various tools that you can use to run email split testing. Some of the most popular ones include:


Mailchimp allows you to quickly and easily create email marketing campaigns. They also offer a split testing feature that allows you to test subject lines, forms names, content, send times and more. Once you have decided on which variable you will be testing, you can build up to three variations per test. You can also choose a sample size and determine which metric will decide the winning version.

Campaign Monitor

You have many options and features to create, send and analyse custom email campaigns with Campaign Monitor, along with the easy running of split tests. You can choose one of their various email templates to create emails matching your branding before using the drag-and-drop feature to add items like call-to-action buttons and images. Once you are ready to send the versions, you can use the custom A/B testing feature to find the best subject line, pick your sample size, and determine your desired outcome.


Convertkit offers an all-in-one platform for all your email marketing and testing needs. It is an ideal solution for start-ups, small businesses and bloggers. The A/B testing feature makes it easy to test different subject lines. All you need to do is enter the different subject lines that you want to test and run the test. Once a few hours have passed, the subject line with the highest open rate will be sent to the rest of your subscribers.

Variables to Test

It’s not always easy to determine which variables to test to help you boost the most important performance metrics. From design principles to subject lines, many different components are part of a successful email. A solid understanding of the key performance indicators (KPIs) and the email components that impact them will help identify what you should be testing.

1 – Open Rate

This refers to the percentage of recipients that opened your email. You can work this out by taking the number of emails that are opened and dividing this figure by the number of messages delivered. If your open rate is low, it’s a good idea to run an A/B test on the subject line or the preheader – the text preview that appears next to or below the subject line in the inbox. Subject lines are essential to the email as they are the first thing people see when the message lands in their inbox.

2 – Click Through to Open Rate

This refers to the percentage of clicks in a message divided by the number of opens. If your click-through to open rate is lower than you’d like, or you want to improve an email, several different aspects of your email body can be tested and improved upon. Eye-catching and engaging content throughout the email will keep subscribers interested in what you have to say. Make sure you create clickable content and consider how information gaps or interactive content could affect the in-email engagement.

3 – Unsubscribe Rate

This is the percentage of recipients who request to unsubscribe from future emails from you. If you have a high unsubscribe rate, then you might be sending email content that isn’t relevant or sending too many emails.

Email Split Testing Best Practices

Email split testing seems relatively straightforward. But with any test, it’s essential to keep some best practices in mind to ensure that your test is valid.

Identify each variable you want to test, and ensure you know what you want to fix regarding your emails before you start running tests. It’s also important to only test one element at a time. Too many different elements in one variation of your email can make it difficult, if not impossible, to determine which one has caused the difference in open rate, click-through or conversions. You should also keep records of the split tests performed, the results, and how the findings will be implemented. Finally, ensure that your sample size is large enough to be statistically significant and completely randomised to get the most reliable results and ensure that your findings are accurate.

A/B or split testing for email is crucial to the success and optimisation of your email campaigns, allowing you to gain insight that can help you make the best decisions regarding your current and future emails. A/B testing is designed to deliver insights that are straightforward yet powerful, allowing you to get better results quickly.

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Line and dots