Email marketing is the only marketing channel that allows you to collect real-time data from your audience. And A/B testing in email marketing offers invaluable insights for your business. These insights will assist you in making data-driven decisions to optimize your email marketing program and get you the ROI you’re looking for. In a nutshell, you’d be crazy not to test everything you possibly can.

Not sure where to start? Think about the different aspects of your email marketing program. Design, content, and other factors that affect engagement, like send times or send days. 

Create tests based on these to see which factors bump up those engagement rates. Once you’ve determined the winners, you can integrate these into your email campaigns going forward.

Here’s an example - for a few brands, we found that including emojis in the subject line increased open rates by up to 10% compared to the SLs without emojis. This was especially relevant for promotional emails. Want to find out if the same is true for your brand? Test!

Looking for more interesting A/B test results? Let’s take a closer look at some case studies based on CodeCrew’s (very!) extensive A/B testing efforts. But first…

A/B Testing In Email Marketing - Why It Matters

Here are just some of the benefits of ongoing A/B testing in email marketing:

  • You’ll understand your audience better: Through A/B testing, you’ll learn what gets your audience clicking and what they don’t enjoy. This information can be applied to future campaigns to improve your audience’s experience and help you rack up those sales.  
  • Find out what your subscribers prefer: A/B testing can help you determine which products or discounts turn leads into customers. And whether presenting your products in a certain way can impact your revenue.  

Email Marketing Case Studies - How A/B Testing Made A Difference

A/B Testing Designs and Layouts

We’re all about bringing communities together, so when we partnered up with Nextdoor, we brought our A-game with A/B testing. By comparing different layouts, we discovered what was missing, and what we could change in order to convert Nextdoor’s leads.

Sip on this! With FinalStraw’s email workflows, we determined which designs their audience responded to best, and what kind of look increased engagement and revenue.

A/B Testing Content

With PetLab Co, we A/B tested whether including the brand’s name in our subject lines or changing send times would impact open rates (spoiler - they did). This made a huge impact on engagement and revenue.

We nailed it with the nail art brand Maniology. By A/B testing their subject lines, pre-headers and send times, we achieved a significant increase in ROI.

Applying A/B Test Results To Get Results

An A/B test a day can keep the unsubscribes away. Which is especially true in the case of the medical supply company Shop Home Med. After tweaking their campaigns based on the data from our A/B test results, we achieved a 114% open rate increase. Plus, an 186% click rate increase, a staggering 228% conversion rate increase, AND a 306% revenue/recipient bump. Last but not least, we also achieved a 24% uptick in average order value. Just what the doctor ordered.

Want to see more examples of how we’ve used data to drive client engagement and revenue through the roof? Check out our email marketing case studies

Insights From A/B Testing

Now that we’ve done a song and dance about the importance of data, it’s time to start A/B testing. Trust us, you’ll be doing your own happy dance once you see the stellar results. To get you inspired, here are some of the tests we've used previously, and their remarkable results.

  • Subject line and pre-header: There are infinite tests you can perform here. Start with emotive vs. straightforward subject lines. We've seen open rates increase by up to 3.5% in either direction's favor, depending on the audience. Secondly, it’s important to test longer vs shorter subject lines, both for promotional and non-promotional emails. We've seen open rate swings of up to 5% in either direction's favor depending on the recipients involved. 
  • Personalization: We've seen that a personalized subject line can increase open rates anywhere from 1% to 5%. And, not mentioning a brand's name in the subject line can actually increase open rates anywhere from 1% to 4%, in our experience.
  • Send times: Invest in finding the right send time for your audience. The best-performing times can vary by audience and can get up to 10% more opens than others.
  • Send days: When launching products (using the same email campaign and send time), we noticed that Thursday had 2% higher opens than Friday.
  • Content: In one client's campaign, we saw a 31.03% difference in open rates between two content-related tests.
  • Buttons and CTA: Changing the wording, shape, or color of your CTA buttons can impact your conversion rates significantly.
  • Test email designs: This can include the hero image, background color, or even the entire layout and structure.

ESPs and Email Marketing A/B Testing - What You Need to Know

When it comes to A/B testing in email marketing, not all ESPs (Email Service Providers) are created equal. Some offer a far wider range of tests you can perform and stronger A/B testing capabilities. These can have a significant impact on the success of your email marketing program. Here are three that will allow you to perform a wider range of A/B tests:


Klaviyo’s A/B testing capabilities include subject lines, send times, and email content. It also allows for multivariate testing, champion vs challenger tests, and the testing of SMS campaigns. What’s more, Klaviyo classifies test results using four groups. These groups are statistically significant, promising, not statistically significant, and inconclusive, to ensure that the results are accurate.


Mailchimp provides A/B testing functionality that’s easy to use and navigate. It also allows you to perform tests based on the amount of revenue generated. However, there are slightly fewer variables that you can test compared to Klaviyo. 


ActiveCampaign offers powerful features that will help you better understand your customers. This includes the ability to test a wide variety of variables, from content to CTA buttons. It also allows you to test up to five emails at once, and perform tests on your automated flows.

And that's just scratching the surface. There are so many Email Service Providers that are great for A/B testing in email marketing. But it's not a one-size-fits-all. The ESP you choose should be determined by your unique email marketing requirements.

The most important thing about A/B testing is this - it takes time. For A/B testing to really work, you need to test every campaign and flow touch, analyze the results, and continually apply your findings to future email campaigns. Which is not an easy job when you're already running a business.

That’s where we come in. Chat with our 'Crew and we'll show you how our data-driven approach can help you skyrocket your ROI.