5 Tricks To Supercharge Email Subject Lines

by Parry Malm, CEO, Phrasee

Parry Malm, one of the speakers for Technology for Marketing, explains how to unearth the secrets to excellent Email Subject Lines.

Email subject lines are important.

This is obvious to anyone works in email marketing… or anyone who has an email address, for that matter.

I mean, consider my inbox:


Not only does this give a keen insight into my personal life… but note two things:

  1. The first thing you notice is the “From” name.

This is obviously super important, and is a signal of brand recognition. But, it’s not something you can just change overnight… because it’s your brand. So, while important, it’s not really an optimisation target.

  1. The second is the subject line.

I get a lot of emails, as do you. And I don’t open some of them. But when I’m in buying mode, the subject line is what gets me across the line.

This begs the question, “What makes a subject line awesome?”

Great question. I get asked that all the time (you’d expect as much, considering I run Phrasee, the robot marketer that writes better subject lines than humans…)

So here are 5 awesome tricks to supercharge your subject lines:

  1. There’s trillions of ways to write a subject line. Which is best?

Many people under-estimate the amount of ways you can write a subject line.

Take, for example, this one:

“Get up to 50% off the latest Batmobiles from Wayne Enterprises – sale ends today!”

Here’s another way you can say it:

“Get half off brand new Wayne Enterprise Batmobiles – sale ends at midnight!”

And another:

“Ends today! ½ price Batmobiles from Wayne Enterprises…”

And another:

“Time for a new Batmobile? Wayne Enterprises is giving you half off… only until midnight”

All of the above are plausible subject lines. But how many more ways can you write the message?

The answer: trillions.

Yep, trillions. Not millions, not billions. Trillions.

There’s way more ways to write this subject line than a human could ever conceive.

And what about picking the best one? Aside from fallible human gut feeling…

Luckily, understanding large sets of language data is something machines are good at – but more on that in a minute.


  1. Short or long? Pro tip: it doesn’t matter!

“I can only see a few characters on my iPhone, therefore the subject line should be short,”

Or so said many an email marketer. And they’re wrong for saying it, and here’s why.

See, subject lines are our thing here at Phrasee. We’ve done the research. We’ve done the stats. We’ve built the models. And guess what?

Subject line length has no effect on open, click or conversion rates.

Take a minute, and digest this fact. Perhaps it’s counter-intuitive, but – and believe me on this – the numbers don’t lie.

I’ll say it again: a subject line’s length has no bearing on its effectiveness.

Why? The full reasoning is far beyond a shot blog post like this. But you can read Phrasee’s full analysis here in The Final Word on Email Subject Line Length.


  1. There’s no “best word ever”.

There’s been some chatter of late about bad versus good words. For example, assuming “brand new” is always better than just plain old “new”.

Well, that’s sort of true, and sort of not true, and here’s why.

For your audience, some words will perform better than others. For example, if you’re selling pretty much anything, calling something “sh*t” likely won’t work so well – unless you’re selling toilets, in which case it may be apropos.

By simply looking at word-level variables (as opposed to more abstract variables like syntax and semantics), you’re using a VERY rudimentary way to analyse a subject line.

It lacks context… but context matters. A lot.

Individual word choice is important, but there’s no single word that’s going to make your subject line the best subject line ever. What’s more important is the interactivity between individual words. The whole, so to speak, is greater than the sum of the parts.

So ignore anyone or anything that says, “Well, I like this word more than that word.” It’s just their opinion, or some really sh*tty “statistics”.


  1. Test your subject lines out. Always.

Let me ask you a question: would you take a pharmaceutical that hadn’t undergone rigorous clinical trials?


So why would you ever send out a subject line that hadn’t been rigorously tested?

Testing is how we learn about the world around us.

It’s how you create sustainable response, revenue and ROI from your email list.

There’s no shortcuts to testing.

And yes, more testing more does mean more work.

But if more testing, and therefore more work, gets you better results…


Isn’t that your job description?

And remember: if anyone ever tells you that split testing is no longer necessary, they are categorically and scientifically wrong. Tell them to have a chocolate drop and go sit in the corner.


  1. Adapt to your audience.

Have you ever sent out a subject line one week, and it worked great, and you sent out the same thing the next week… and it sucked?

That’s annoying, right? Wouldn’t it be great if life were easy and predictable?

Here’s the thing. People change. Your audience changes. The world around you changes.

Michael Phelps isn’t known for treading water. He’s known for adapting his training routines, his swimming techniques, and his evil stares, based upon numerous external factors.

Phelps email marketing

Adapting to your customers wants and needs is the absolute key. Understanding what those wants and needs are difficult to quantify. But – this understanding is key to making your subject lines get results.


  1. AND A BONUS #6 – come meet the machine can write better subject lines than you!

Writing subject lines is hard… and they’re the most scrutinised part of an email campaign. I mean, if your CEO ever comes downstairs to give you crap about an email, 95% of the time it’s about the subject line.

See, when a subject line is good, awesome sauce. But when it sucks, it costs you real, cold, hard cash.

Writing a good subject line is hard because there’s literally trillions of ways to write it. So what are the odds that you get it right? Infinitesimal. There’s too much data for a human to process.

Luckily – this is exactly what machines are good it.

Meet Phrasee – A.I. that writes better subject lines than humans.

Come say hi to us at TFM and see how the magic happens!

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