How to Write Email Subject Lines That Get Opened (Without Being Clickbait)

You can build the most beautifully designed email with the most compelling offer and the most persuasive copy. If the subject line doesn't get opened, none of it matters.

The subject line is the gatekeeper. It determines whether the hours you put into an email campaign generate revenue or sit unread in an inbox.

After sending hundreds of campaigns across multiple Shopify brands, we've identified the patterns that consistently outperform — and the common mistakes that kill open rates.

The 3-Second Rule

Your subject line gets approximately 3 seconds of attention. That's how long someone glances at their inbox before deciding to open, skip, or delete.

In those 3 seconds, your subject line needs to accomplish one thing: create enough curiosity or urgency to earn the click. Not convey the entire message. Not explain the offer. Just earn the open.

Everything else happens inside the email.

The 5 Patterns That Consistently Win

1. Specific Numbers

Numbers cut through noise because they're concrete. The brain processes specific numbers faster than abstract claims.

"3 products under €25 for weekend gifting" outperforms "Check out our affordable gifts."

"We just restocked your #1 favorite" outperforms "Back in stock now!"

The specificity signals that there's real information inside the email, not just generic marketing.

2. Curiosity Gaps

A curiosity gap is when you reveal enough to be interesting but not enough to satisfy. The open becomes the resolution.

"The one thing we changed that doubled conversions" works because the reader needs to open to find out what "the one thing" was.

The key is authenticity. The email has to deliver on the curiosity. If your subject line promises a revelation and the email is a generic product push, you'll get opens once — and then subscribers learn to ignore you.

3. Direct Benefit Statements

Sometimes the best subject line just tells people what they get.

"Free shipping this weekend only" works because the benefit is immediate and clear. "Your skin will thank you" works because it connects the product to the outcome the customer wants.

Direct benefit lines work particularly well for engaged segments who already know your brand. They don't need to be seduced — they need a reason to act now.

4. Urgency (When It's Real)

"Last 6 hours" works. "Sale ends tonight at midnight" works. "Only 12 left in stock" works.

But manufactured urgency destroys trust. If every email has a countdown timer and every sale is "ending soon" but never actually ends, subscribers learn that your urgency is fake. When you have a genuinely time-limited offer, they won't believe you.

Reserve urgency subject lines for moments when the urgency is real. Use them sparingly — 2-3 times per month maximum — and they maintain their power.

5. Personal and Conversational

Subject lines that sound like they came from a person outperform those that sound like marketing.

"I think you'd love this" outperforms "New arrivals just dropped!"

"Quick question about your last order" outperforms "Post-purchase follow-up."

This pattern works because email is inherently personal. It lives alongside messages from friends and colleagues. Subject lines that match that conversational context feel native rather than intrusive.

The Mistakes That Kill Open Rates

ALL CAPS and Excessive Punctuation

Writing "HUGE SALE!!!! DON'T MISS OUT!!!" doesn't convey excitement. It conveys desperation. And it triggers spam filters. Gmail's algorithms are specifically trained to flag excessive caps and punctuation as spam signals.

Lowercase or normal capitalization consistently outperforms all-caps in our A/B tests.

Being Too Clever

Wordplay and puns can work for brands with a playful voice. But if the subject line requires a moment of decoding, you've lost the 3-second window.

"Blanket statement: our new collection" might get a smile from some. But "Our softest blanket yet — just launched" is clearer, faster, and more likely to drive an open.

Clarity beats cleverness in e-commerce email.

Misleading Subject Lines

A subject line that says "Your order has been updated" when it's actually a promotional email will get opens. It will also get spam complaints. And it will erode trust faster than almost anything else you can do.

The subject line is a promise. The email is the delivery. If the delivery doesn't match the promise, you lose.

Ignoring Preview Text

The preview text (the line that appears after the subject line in the inbox) is the most underused real estate in email marketing. Most brands leave it as the default — which shows the first line of the email body, often "View this email in your browser" or the alt text of the first image.

Treat preview text as an extension of the subject line. If the subject line creates curiosity, the preview text adds context. If the subject line states a benefit, the preview text reinforces urgency.

Subject: "Your new favorite — just arrived"

Preview: "We made 200. They won't last."

That combination works harder than either line alone.

The A/B Testing Protocol

Subject lines should be your first and most frequent A/B test. Here's the protocol that produces reliable results:

Sample size: Minimum 1,000 subscribers per variant. Below this, the results aren't statistically meaningful.

Duration: Let the test run for at least 4 hours before declaring a winner. Open patterns vary by time of day.

Variables: Test one thing at a time. If you're testing curiosity vs. direct benefit, keep the length, punctuation, and personalization the same. Otherwise you don't know what actually moved the needle.

Testing priority: Subject line first. Always. It has the highest impact on overall campaign performance. After you've optimized subject lines, move to hero image, then CTA, then offer.

Documentation: Record every test result. After 20-30 tests, patterns specific to your audience emerge. Some audiences respond better to questions. Others prefer statements. You won't know until you test consistently.

Length: Shorter Usually Wins

Mobile displays show approximately 30-40 characters of a subject line before truncation. Desktop shows more, but most email opens happen on mobile.

Our data shows that subject lines between 25-45 characters consistently outperform longer ones. This isn't a hard rule — some longer subject lines work brilliantly. But if you can say it shorter, say it shorter.

Test truncation by sending yourself the email on your phone. If the most important words are cut off, rewrite.

The Bottom Line

Subject lines aren't creative writing. They're conversion optimization. The goal isn't to be clever or comprehensive — it's to earn an open from a person who has 3 seconds and 50 other emails competing for their attention.

Use specific numbers. Create curiosity gaps. State benefits directly. Deploy urgency honestly. Write like a human.

Then test everything. Because your audience's preferences are the only opinions that matter, and the data will tell you what works.