Email Marketing: Subject Line Testing 101

subject line testing

With email marketing tools like MailChimp, it’s easier than ever for digital marketers to perform subject line testing, content testing and email performance analysis. Just because you have the means to test, though, doesn’t mean you necessarily understand how and when you should test the variables of your email blasts. In a series of upcoming posts, we’ll take a closer look at A/B testing for emails. First up, A/B split subject line testing.

When should I test my subject line?

April Wilson, President of Digital Analytics 101, says that all A/B tests and optimizations should start at the same place — data analysis. “Typically, a marketer should use the data to figure out the best place to start with their A/B testing. The first thing they should do is trend out their email open rates and interaction (click) rates over the last 6-12 months. Is your open rate declining? Then it’s time to A/B test your subject line.”

Why should I test my subject line?

Although A/B subject line testing seems pretty simple, as JT Capps, Senior Director of Demand Generation at Swiftpage, describes, it’s actually a small part of a larger, overarching process known as Creative Optimization. “Creative Optimizations [consists of] tests done in quick timeframes to identify optimum creative for individual emails. Optimization consists of small iterative tests that over time add significant value by focusing on key performance indicators such as Open Rate, Click-through Rate, Click-to-Open Rate and Conversion Rate.”

Capps explains, “Subject line testing is generally focused on achieving insights and understandings to the effectiveness of different tactics which can influence open rate performance at the TOP of the conversion funnel. [It] is one of the easiest [tests] to execute because it requires relatively little extra operational support to execute. It’s no coincidence that subject line tests are the most popular test type run by email marketers because they can have the most significant impact on overall campaign performance – after all, if the email isn’t opened, the rest of the key performance indicators from clicks to conversion cannot be achieved. So testing tactics which drive engagement at the top of the conversion funnel can have big returns with relatively little additional effort to understand and benchmark potential lift in behavior across unique subscriber segments.”

How should I test?

Julian Dutton, marketing manager at CardFellow, suggests taking a more general approach to the testing process. “In my experience, testing subject lines shouldn’t be done to satisfy a particular campaign. Try to broaden the test so that it may be useful for other things. For example, if you had a product that you wanted to offer a discount on. You could try different approaches to the subject line; ex. ‘take 25% off the product,’ ‘for a limited time get 25% off the product,’ ‘today only,’ etc. The results from these subject lines can be used to help predict what might work well for other products. So, if you see that ‘for a limited time’ works well for one product, chances are it will work for a different product.”

Dutton reminds marketers, “You always want to be testing, but creating the test so that it can help narrow down particular phrases or calls to action is a great way to thin out the subject lines you know won’t work well.”

Looking for a place to start? Check out these must-avoid subject line phrases for both B2C and B2B brands.