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Subject line testing is one of the easiest and most popular practices for successful email marketing. In fact, 83% of marketers believe testing subject lines is the most effective method to optimize emails.1
The logic behind this belief is fairly obvious. Subject lines enjoy prominent placement and therefore have a huge impact on open rate performance. Less obvious to many marketers is the influence subject lines have on other performance metrics.
Consider this: An effective subject line does more than persuade recipients to open. A subject line can also influence your audience’s receptivity to the email content and their decision to take action. So if subject line performance is based solely on open rate, the true impact of the message is not being recognized. Comprehensive analysis should include multiple key performance indicators, such as clicks and conversions.
This successful email marketing practice is best illustrated with an example. Recently, we conducted a subject line test on a welcome email. The goal of the email was to persuade new customers to start using their account. Half of customers received Subject line A; the other half received Subject line B. Aside from the subject line, all other email content was exactly the same. However, the emails performed very differently.
Subject line A
Subject line B
Here are the results.
Subject line B drove 2% more conversions than Subject line A. Based on the sample size of the test, the difference was significant.
Subject line B also converted significantly more email openers, even though the content of both emails was exactly the same. The lift was 4%—even stronger than the overall conversion rate.
It’s clear from this example that a subject line can affect the mindset and behavior of your audience. Subject line B openers were more receptive and ready to take action than recipients of Subject line A. This definitely shows why measuring conversion rate is a successful email marketing best practice for subject line evaluation.
Subject line B had a slightly higher click-to-open rate than Subject line A, but the difference was not significant. Now you may be asking: How did Subject line B drive more conversions, but not more clicks?
There are a number of potential explanations. One reason is that many people are anxious about clicking email links. Email recipients often open, read and take action without ever logging a click. They prefer to enter a URL directly into their browser or use a saved bookmark rather than click an email link.
Despite this, click-to-open rates should always be considered when evaluating a subject line’s performance because it is an excellent gauge of audience receptivity and engagement.
You might assume that the subject line with the most conversions—Subject line B—had a higher open rate. But actually, Subject line A had significantly more opens. This perfectly demonstrates the various ways that subject lines impact multiple email metrics and how focusing too much on open rates could lead you to wrong conclusions.
Another word of caution: Do not interpret open rates as hard facts. An open is only recorded if email images are loaded. Many email clients block images or have preview panes that automatically display an email with images. Thus, a successful email marketing best practice is to interpret open rates as benchmarks rather than facts.
It’s not all about opens
Although Subject line A had more opens, it was not the winner of this test. The objective of the email was to drive customers to start using their account. Thus, Subject line B won with a higher conversion rate.
This example illustrates an important lesson. Although subject line testing is vital to successful email marketing, you will only see positive results if you base decisions on the right facts. It’s important to take a holistic look at subject line performance and not put too much emphasis on open rate. Otherwise, you might inadvertently trade a few more opens for fewer conversions.
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1. Lyris, ”The Lyris Digital Optimizer Report,” 2012
Topics: Email Marketing