Boost email opens 18% with this simple rule

Today I want to introduce an important part of email marketing that doesn’t get enough attention: Crafting subject lines that actually get opened.

Your subject line can literally make or break the success of any email you send. But we often leave the work of choosing a subject line to the very end of the writing process - almost like an afterthought. And this is a huge mistake.

So I want to get you thinking creatively about this powerful detail in your emails. Because I’d argue the subject line might be the most important part of your email, and worth defining before you write anything else.

I mostly focus on email subject lines when I’m working on this newsletter. But you can apply this lesson to any kind of email outreach that you do.

And as they say, the devil is in the details.

So let’s dive in.

The Curiosity Gap

Analyzing the last 130+ newsletters I’ve published, I've identified a pattern. The emails with the highest open rates almost always have one thing in common:

They employ the "Curiosity Gap" technique in their subject lines.

The Curiosity Gap is a simple way to introduce what your email is about and pique interest to learn more.

Here’s a 5-part strategy for using this technique to create irresistable email subject lines:

Part 1: Identify a Common Pain Point

Start by pinpointing a specific problem your audience faces.

The easiest way to do this is to talk to them — what are the most common pain points you hear from your audience when you’re interacting?

For instance, if you're in the fitness niche, a common issue might be "struggling to lose those last five pounds."

This is a great starting point.

Part 2: Hint at a Solution

Next, hint at a solution, but don't give it away entirely.

This creates that "Curiosity Gap" — the space between what your reader already knows and what they want to know.

Getting this right will increase your email open rates because it teases a solution to the very specific problem you’ve learned about.

Part 3: Use Numbers

People love specificity.

Numbers in subject lines tend to perform well because they promise concrete information.

But round numbers (like 10% or 20 minutes) don’t perform as well as non-round numbers (17% or 29 minutes).

It makes sense if you think about it. We’ve been inundated with 10% and 30% discounts, improvements, etc.

A number like 17? Or 29? Those are much more eye-catching and harder to ignore in a world of zeros and fives.

Part 4: Keep it Short

Aim to keep your subject line at 50 characters or less (including spaces and punctuation).

That seems to be the cutoff point for subject lines that perform well and those that don’t.

This mostly has to do with how many characters different email platforms (like Gmail) show in the inbox. It’s obviously going to be different for mobile and desktop, but I’ve found that once I cross 50 characters, my open rates drop.

Note: There are a ton of studies on this, and they all come to slightly different conclusions. This is what works for me, so be sure to test your lengths to see what resonates with your audience.

Part 5: Avoid Spam Trigger Words

Words like "free," and "guarantee," can trigger spam filters and send an otherwise perfect email straight to spam folders, even if a reader wants to get your message.

So instead, focus on value-driven language.

Here's an example of how this might look:

Bad subject line: "Free weight loss tips inside!"

Good subject line: "The 3-minute trick that melts away stubborn fat"

Let's break down why the second subject line works:

• It addresses a pain point (stubborn fat)
• It hints at a solution without revealing it (a ‘trick’)
• It uses a specific number (3-minute)
• It's pretty short (47 characters long)
• It avoids spam trigger words

Experimenting With Subject Lines

In a recent A/B test I ran, emails using the Curiosity Gap technique had an average open rate of 52%, compared to 44% for standard subject lines that didn’t employ the technique.

That's an 18% increase in opens - an important difference.

I hope you’ll give the Curiosity Gap technique a try, and analyze your own results. But remember, a great subject line is just the first step.

Your email content has to deliver on the promise your subject line makes. Otherwise, your open rates will plummet over time, as subscribers feel misled or cheated.

Action Step For This Week:

Take your next five email subject lines, and rewrite them using the Curiosity Gap technique. Then, A/B test them against your standard subject lines. Track your open rates and see the difference for yourself.

If you implement the Curiosity Gap technique, I'd love to hear about your success. Send me an email and tell me how it went.

And if you want to dive deeper into email marketing strategies that actually work, check out The Creator MBA. There's an entire module dedicated to building and monetizing your email list, including advanced segmentation techniques that can boost your conversion rates by up to 355%.

Join 4,000+ other entrepreneurs who are already seeing results.

That’s all for this week.

See you next Saturday.