[FAQ]

Hey everyone, I have a question about optimizing my email campaigns.

I know I should be A/B testing my emails to improve them, but I’m not sure how to do it effectively.

What are the best things to test – subject lines, send times, content? And how does the process work? Do I need to have a huge list for the results to be meaningful? I’m looking for some best practices for 2025 on how to set up, run, and interpret A/B tests to get real, actionable insights.

Thanks for any advice!

[Jeff Bullas]

That is a smart question to ask. Moving from guesswork to data-driven decisions with A/B testing is what separates a good email marketer from a great one.

The process is about scientifically comparing two versions of a single email to see which one performs better. To do it effectively, you need to be methodical.

Here are the key practices to follow. First, and this is the golden rule, you must test only one single variable at a time. If you change both the subject line and the main image in your test, you will have no idea which change was actually responsible for the difference in performance. You must isolate your variable.

Second, you need to decide what to test. The most common and often most impactful element to test is the subject line, as this directly affects your open rate. Other high-impact elements include your call to action (CTA) wording or button colour, the email’s main headline, or even the “from” name you use.

Third, you must define your success metric before you start. If you are testing a subject line, your success metric is the open rate. If you are testing a call to action, your success metric is the click-through rate. Knowing what you are measuring is crucial.

Fourth, you need to ensure your test group is large enough to be statistically significant. Most email marketing platforms will handle this calculation for you and tell you when a winner has been determined. Testing on a very small list can give you unreliable results that do not hold true in the long run.

And fifth, you should let the test run for long enough to gather meaningful data. You need to give subscribers a reasonable amount of time to open the email. A typical test duration is anywhere from four to 24 hours before your email platform declares a winning version and sends it to the rest of your list.

In summary, effective A/B testing is a methodical process. You should test one variable at a time, have a clear success metric in mind, use a large enough sample size, and then apply what you learn from the winning version to inform your future campaigns.

Cheers,

Jeff

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