A/B testing email subject lines
Have you ever had an email with an open rate of 104 percent?
Wait, is that even possible? How can you have an open rate higher than 100?
I have yet to achieve the mythical, 100+ percent open rate (my best is a unique open rate of 82%), but it is possible to do. If you’re tracking total opens instead of unique opens, if a ton of people open your email multiple times and forward it to their friends…you can record an open rate above 100%.
But the most incredible thing about a 104% open rate email—which is real, and was written by copywriter Joanna Wiebe—isn’t the sky-high open rate.
It isn’t even the sky-high conversion rate of the funnel as a whole.
It’s the fact that the email was almost never sent at all.
As Joanna recounts in a talk for the Business of Software, she expected the email to be a flop. The tone of the email made her uncomfortable, and she was seconds away from deleting it—until she looked at the analytics.
On a list of thousands and thousands of people, this email was most definitely pulling its weight (unique opens were also high, in the high 80s).
But without the data, it would have disappeared.
And without the lessons learned from A/B testing, it never would have been successful in the first place.

A/B testing subject lines helps people listen to you

Your email open rate is affected by lots of factors. Deliverability, from name, time of day, and preheader text are all important—but no factor is quite as important as your subject line.
Your email subject line is what draws people in. It’s where you have the chance to grab attention and force people to click with the power of curiosity.
It’s what gets people to listen.

On a list of 10,000 people, an open rate of 20% gets you 2,000 readers. If you can bump that up to 25%—which is totally possible with a great email subject line—you’ve earned another 500 readers.
Even at a meager 1% conversion rate, that’s 5 new customers.
All of that, from changing the subject line of one email. What if you could write better subject lines for every email?
Picking winning subject lines is difficult, but A/B testing makes it a whole lot easier.
A subject line test is simple: You send the same email to small portions of your list. Look to see which group opened your email more often, then send the winning subject line out to everyone.
Can it get more complicated than that? Of course.
You can test subject lines against multiple different variants. You can adjust the size of your list that you use to test subject lines. You can wait longer before choosing the winner. You can judge the winner based on click through rate instead of open rate.
ActiveCampaign split testing example
All of that is worth doing—eventually. But you don’t need to start with a super complicated split testing system.
Early on, it’s enough to run simple A/B subject line tests. One subject line vs another. Mano a mano. A duel to see which subject line is the most enticing.
A/B testing email subject lines is easy, from a technical standpoint. Just a few button clicks.

These are the 6 email campaigns you can send in ActiveCampaign

Split tests are one of the 6 campaign types in ActiveCampaign. This video, from the free course Getting Started with ActiveCampaign, shows just how easy it is to set up a split test email (literally a few clicks). 

The much harder question is…what should you test?
When you A/B test subject lines, it’s easy to come up with any-ole sentence to throw at the test. It’s a lot harder to come up with a test that you can learn from—and make all of your future subject lines better too.

This article will help. We’ll walk through the fundamentals of great email subject lines, talk about which tests to run, and give you some templates that you can steal to use right away.
You’ll learn

  • The psychology of curiosity, and the mistake most subject lines make (but yours can avoid)
  • How to pinpoint the emotions you want to create in your audience
  • Tests you can run in your next email
  • Exact subject line templates you can steal (and examples of them in use)

We’ll start by talking through a pair of powerful fundamentals.
Why? Because even though testing is important (and the best way to find the best email subject lines), you can skip huge frustrations by learning from those who came before.

The Curiosity Gap and the power of strong emotions

In 1994, Carnegie-Mellon professor George Loewenstein published an extraordinary paper with a mundane title: The Psychology of Curiosity.
In the paper, Loewenstein proposed the “information-gap theory” of curiosity. I’ll spare you 25 pages of dense psychology writing and give you the short version—we (humans) are curious when there’s a gap “between what we know and what we want to know.”
Curiosity, in turn, makes us take action to find answers.
Stepping back into the world of marketing, your email subject lines will be enormously more effective if they can make people curious.
And yet…
Too many marketing emails don’t bother with curiosity. Instead, they make a mistake that’s killing their open rates (and might be killing yours).
Your subject line should not summarize the content of your email.
This is so important that I want to say it again: your subject line should not summarize the content of your email!
Imagine your email has landed in someone’s inbox. They’re about to check for new messages. They check, and see your subject line. This is it—the moment of truth.
But your subject line gives them all the information they need. It tells them exactly what to expect from the email, so they don’t bother to open your message (and certainly don’t click). They’d much rather read through the pun chain going on in the latest reply-all.
Instead of telling people exactly what to expect, get them curious.
The biggest rule of email subject lines? Tease, don’t tell.

Expert Insight: Rob Marsh on getting opened

Photo of Rob Marsh, conversion copywriter and marketing strategist
“Remember the purpose of a subject line is to get the email opened.
Just about everyone will open an email from their mom or their friends—regardless of the subject line—because we have a relationship with these people.
But emails from businesses or someone we don’t have a personal relationship with? The subject lines on those emails need to give us a reason to open them.
They need to create curiosity. Or pique our interest. What they shouldn’t do it make a pitch. A subject line won’t make the sale, so don’t try. They simply exist to get the email opened.
Then you hit them with brilliant copy that agitates the pain they feel and intensifies the need for the product/service/message you have to share.”
– Rob Marsh is a conversion copywriter and marketing strategist who works with health, tech, and SaaS companies to tell their brand stories. He writes at BrandStory and runs The Copywriter Club podcast.

Loewenstein lists 5 ways that you can create curiosity.

  1. A curiosity-inducing question
  2. A sequence of events that is left unfinished (with an unclear outcome)
  3. A violation of expectations
  4. When someone else has information we are lacking
  5. When we used to have information that we’ve since forgotten or lost

Let’s take a look at an example, so you can see this in action. Which of these is the most compelling?

  • How to earn half a million dollars a year
  • How can you earn half a million dollars a year?
  • Do you have the courage to earn half a million dollars a year?

Right off the bat—it isn’t number one.
Number one makes a big claim, and it summarizes. If you saw that in your inbox, you’d probably dismiss it as a scam or exaggeration from some marketer.
Number two is a bit better. It’s still a bit over the top, but it at least asks a question. Still, it doesn’t really violate expectations. And even though it implies I have information you don’t, it makes that information seem unbelievable.
But number three…
Number three was written by legendary copywriter Eugene Schwartz, as the headline of a mail-order advertisement for a book on investing (old-school headlines and email subject lines have a lot in common).
Schwartz has added another one of Loewenstein curiosity-inducers—violated expectations. When I read that headline, I’m no longer thinking about the over-the-top claim ($500,000 per year). I’m actually asking myself if I have courage.

Which brings us to the next point—strong emotions.

Expert Insight: Laura Belgray on intimacy

Laura Belgray of Talking Shrimp
“What will pop out from all the other businessy-looking garbage in your subscribers’ inbox, and what will feel most “me to you” intimate?
When it’s a really important email, I’ll send myself a test to see how the subject line looks on my phone — and how much of it shows up. The first words are the most important, because the rest is often cut off.”
– Laura Belgray is a copywriter and founder of Talking Shrimp. You can learn how to write high-converting emails with her guide to subject-line writing.

Gary Bencivenga, perhaps the greatest living copywriter, has this to say about the power of emotion in advertising.

“The vast majority of products are sold because of the need for love, the fear of shame, the pride of achievement, the drive for recognition, the yearning to feel important, the urge to look attractive, the lust for power, the longing for romance, the need to feel secure, the terror of facing the unknown, the lifelong hunger for self-esteem and so on.

Emotions are the fire of human motivation, the com