Our Blog

“Knowledge is knowing a tomato is a fruit. Wisdom is not putting it in a fruit salad.”


  • Categories

Search Blog

The AI subject line hack that supercharges email open rates

Nothing beats a good hack.


Discovering one of your own is one of life’s best little pleasures.

A simple little adjustment to the way you perform a mundane, inconvenient, or difficult everyday task can make all the difference in the world.

So it is with email subject lines.

Email marketers write a lot of subject lines over the course of their email marketing careers. Some will perform well and make money, others, not so much. With only experience and gut feel to guide subject line content decisions, getting them right all the time is a tall order indeed.

If ever there were a repetitive task just begging for some quality hack-action, writing email subject lines is it.

Is the word “hack” a little overused these days? Sure, but does that mean it is never relevant? We certainly don’t think so.

So “hack” it is.


The AI subject line hack that supercharges email open rates


What’s in a subject line?

There is no email marketing performance metric in existence with a direct impact on overall email marketing performance quite like that of the mighty open rate. No matter how well an email is designed and developed, no matter how finely crafted its body content, no matter how enticing the generous offers contained within may be, if no-one opens it, all the efforts of the team that designed it will be for nought.

That’s why it is so crucially important to get the subject line right.

According to data from Return Path, the average email marketing subject line is between 41 and 50 characters long. Contained within those characters are the thousands of linguistic variables which allow any subject line’s message to be constructed in a multitude of different ways.

With so many variables at play in any given email subject line, what are the odds that any human on earth, no matter how skilled, will get her subject line language right 100% of the time?

Pretty slim.

That’s what got us here at Phrasee thinking: maybe the best email subject lines humanly possible weren’t good enough. maybe a machine could do better.


A new era of subject line optimisation technology

Artificial intelligence is awesome. In seconds it can analyse volumes of variables and data that would take even the most capable human weeks to sort through.    

To a machine, the linguistic variables involved in constructing an effective email subject line are nothing more than elements in a mathematical equation.

The tricky part is determining what problem the AI’s mathematical equation should be solving.

For email subject lines, we teamed up with our AI language optimisation tech to look at 3:


Deep learning for better performance

Every brand’s audience responds to different subject line language in different ways.

AI can be trained to analyse a brand’s subject line performance data and use the results to generate subject lines specifically designed to engage that brand’s audience. AI can continue to learn based on the performance data it collects, optimise the language it generates accordingly, and get better at generating that language as it goes.


Performance prediction

Being able to predict how a subject line will perform for a specific brand on its audience is a huge competitive advantage.

With enough subject line performance data to look at, AI can be trained to predict with an astounding degree of accuracy how a brand’s audience will respond to an email subject line before it is even sent.


Ongoing testing at scale

Modern email marketing audiences are fickle.

What works on a brand’s audience today may not work on that same audience a week later. That’s why it is of crucial importance that every brand test and monitor the performance of its subject line language on a consistent and ongoing basis. AI can take on and manage this arduous task, conducting regular tests to make sure that the subject lines it is generating continue to engage the audience it is studying.


AI isn’t a perfect solution to every problem in the world, but it has proven to be ideal for generating effective, engaging subject lines that make brands more money.

If you’d like to hear more about what AI-driven subject line optimisation can do, we’d be more than happy to show you, book a demo today!

Sign up to Phrasee’s weekly newsletter. It’s awesome. We promise.

Discover how applying actual AI to language can deliver big results!