Resources Home

Measure Every Email Metric, Not Just the One You’re Testing

Published by Jeff Giddens

Testing one element of an email can impact all of your email metrics. For example, even though a subject line might seem to directly correlate with your open rate, it could also be affecting other downstream email metrics like clicks and conversions without you knowing it.

In this email below, the subject line reads, “Supporter Match Status: Active.” Honestly, it sounds like a robot wrote this subject line. I’m not entirely sure what it means.

Email Metrics - Example 1

As you can see, there’s disagreement between the subject line, the copy, and the call-to-action. And the initial impression that the subject line leaves me with affects the way I read and perceive the rest of the email.

In regards to the subject line, I wonder, is this actually leading me through the mental conversation you want me to have? When I initially read the copy, I immediately noticed that there was something off between the subject line and the copy. The subject line sounded like a robot, but then that robot was suddenly telling me that we’re friends.

In the end, I deleted the email.

How subject line clarity affects email click-through rate

Experiment #4057

Subject lines and calls-to-action are closely related. This is an email we tested for a church in Vancouver called First United that ministers to the homeless.

Experiment 4057 - Email Metrics - Control

In the control, the sender was “First United.” The subject line was informative and cheery, but it didn’t give much incentive to open or click.

In the treatment, the subject line includes a call-to-action. It prompts the reader to ask what it means to join, how to join, or what they’d be joining.

Experiment 4057 - Email Metrics - Treatment

Interestingly, the treatment didn’t produce a significant increase in open rate. But, it’s always important to look at all of the email metrics to see what affect your changes may have had downstream. In this case, the treatment produced a 42.2% increase in the click-through rate, despite having no significant affect on opens.


Everything about the email remained the same except for the subject line. But by asking people in the subject line to join, we got more people to take action. This shows us that, again, subject lines don’t live in a vacuum. Agreement between the subject line and the call-to-action can have a significant impact on the likelihood that the recipient will take the intended action.

What we’re seeing from these examples is that your subject lines should incentivize people to open your emails. We also need to measure all email metrics along the journey! If we don’t also look at clicks and conversions when we test subject lines, we may actually be dis-incentivizing people from clicking through our emails and taking the actions we want.

Multiplying the effectiveness of your emails

6 Ways to Grow Your Email FileBy aligning your email subject line and call-to-action, you can test your way to higher opens, clicks, and conversions. But higher conversion rates have an even greater impact when you have a larger volume of traffic.

Time and time again, we see that the size of an organization’s email file is the number one indicator of their ability to raise money online. So if you can acquire more emails, you will acquire more revenue.

Learn 6 ways to grow your email file, and lift your online revenue by downloading your copy of this free eBook.

Published by Jeff Giddens

Jeff Giddens is President of NextAfter.