A/B testing is a wonderful thing. It allows you to see how different subject lines, CTA buttons, content and delivery times can all individually affect your subscribers engagement rates. A/B testing has always been a great way to gain insight into your customers’ preferences and engagement tendencies, but how can marketers take advantage of A/B testing in email campaigns? Let’s find out!

Subject lines

Subject lines are vital to any email due to the increasing competitiveness of email marketing, which often makes for an overcrowded inbox.

Numerous studies have focused on the optimal length of subject lines with no definitive conclusion. The only thing that seems certain is that it’s best to have either very short (under 49 characters) or very long (up to 70 characters) subject lines. Begin by testing shorter subject lines against longer and see which your audience prefers, you may also want to consider the timing variable depending on the topic. For example a “Rough day?” subject line sent at 4PM on a Monday will likely prove a popular choice!

If you think your brand image is more formal, surprise your customers and try an A/B test with a slightly more casual approach. You can still fit the essential information into these informal subject lines so you stay relevant, but being a little unconventional can really help grab your readers’ attention.


Once you’ve achieved the elusive open, will your subscribers read the rest? First impressions count and while you may be tempted to get fancy with your emails by using eye-catching templates, a simpler email might prove the better option.

Photos and videos perform better than virtually all other forms of content. If your subscribers email client blocks images by default, like Gmail tends to do, their experience will be poor so A/B testing is critical. It’s also worthwhile to check how your email performs on different platforms, as approximately 53 percent of emails are opened on mobile devices. If your subscribers can’t read your email, why send it?

Call to Action

So they’ve read your email, and now we want to know whether the CTA will draw them in. Although best practices say you should have one obvious CTA button, multiple ones may create better results. Your choice of wording could also prove your downfall, as sometimes the word “free” in subject lines and CTA buttons is blocked by spam filters. Instead, use a friendlier substitute, such as “complementary”, “on the house” or “as a gift”.

Timing is everything

The time you send your email can mean the difference between being binned and landing a customer. If you’re a B2B brand, you might see more success with an email sent during office hours, whilst a retail brand may get more attention on weekends. It depends on your customers and their daily schedules so test your campaign over weekdays versus weekends to determine which yields the best results. The same rules apply to the time of day; others may tell you that early morning is best as most people check their emails first thing, others will say that late evening or night is better, especially if your readers are attached to their mobile devices. Try segmenting your customers to make this process easier, or utilise an advanced timing control to manage different time zones if you are international.

Will your readers unsubscribe if you email them everyday? Will they get disengaged if you only reach out once a week? Instead of sticking to a frequency you think may work, segment your list and test the open, click-through, and unsubscribe rates to see which frequency of email reaps rewards for your brand.

Final Thoughts

Utilise our 4 stages of A/B testing one at a time and compare your campaigns to analyse the behaviour of your subscribers. You will discover which subject lines, links, content and delivery times within your campaigns prove most popular. Analysing your campaigns are key to improving your customer experience and thus increasing your ROI. To go one step further, review the location and performance of links used within each combination and if your campaigns have the same links throughout, identify which drove the most clicks to determine the best campaign template for future emails. Never stop testing, and never trust a hypothesis or best practices when you can run your own A/B tests and find out the truth!