How to Write Email Subject Lines That Actually Get Opened

You have about 2 seconds to convince someone to open your email. That's the job of your subject line — and most marketers are terrible at it.

The difference between a good subject line and a great one can be a 2x difference in open rates. Over thousands of emails, that's the difference between a thriving email program and one that's slowly dying.

Here's how to write subject lines that actually work.

The Psychology of the Open

People open emails for three reasons:

1. Curiosity — "What is this about?"

2. Self-interest — "What's in it for me?"

3. Urgency — "I need to act on this"

Every great subject line triggers at least one of these. The best trigger two. Here's how to use each one.

The Curiosity Gap

Curiosity is the most powerful driver of opens. The "curiosity gap" is the space between what someone knows and what they want to know. Your subject line should create that gap without giving away the answer.

Examples:

• "The email mistake that cost us $12,000"
• "I was wrong about open rates"
• "This changed how I think about automation"
• "We almost didn't launch this"

Notice how each one makes you want to know more. They hint at something interesting without revealing it.

The trap: Don't create curiosity that your email doesn't deliver on. Clickbait subject lines get opens once. Then they get unsubscribes.

The Self-Interest Play

People care about themselves. Subject lines that clearly communicate a benefit perform consistently well because the reader immediately sees what they'll get.

Examples:

• "3 automations that run while you sleep"
• "Cut your email production time in half"
• "Your open rates are leaving money on the table"
• "The template that generated $4,200 last month"

The key is specificity. "Improve your marketing" is vague and ignorable. "Cut your email production time in half" is specific and compelling.

Creating Urgency (Without Being Spammy)

Urgency works when it's real. Fake urgency ("LAST CHANCE!!!") destroys trust. Real urgency creates a genuine reason to act now.

Good urgency:

• "Sale ends tonight at midnight"
• "Only 3 spots left in the workshop"
• "Your trial expires tomorrow"

Bad urgency:

• "ACT NOW BEFORE IT'S TOO LATE!!!"
• "URGENT: Open immediately"
• "You're about to miss out on everything"

Use urgency sparingly. If every email is "urgent," none of them are.

7 Subject Line Formulas That Work

1. The Question

Questions naturally create curiosity and engagement. The reader's brain automatically tries to answer them.

• "Are you making this segmentation mistake?"
• "What's your email sending costing you?"
• "Ready to automate your welcome series?"

2. The Number

Numbers stand out in an inbox full of text. They also promise a scannable, organized email.

• "5 flows every store needs (and 2 you don't)"
• "3 minutes to set up abandoned cart recovery"
• "We analyzed 1M emails. Here's what worked."

3. The How-To

Directly promises value. Works best when the outcome is specific and desirable.

• "How to double your click-through rate"
• "How to write emails people actually read"
• "How to set up automations in 10 minutes"

4. The Personal Touch

Subject lines that feel like they came from a friend, not a brand.

• "Quick thought on your last campaign"
• "Saw this and thought of you"
• "Can I ask you something?"

5. The Contrarian

Challenge conventional wisdom to stand out.

• "Stop A/B testing your subject lines"
• "Why your best customers don't open emails"
• "The case against email personalization"

6. The Announcement

Straightforward and effective when you have genuine news.

• "Introducing: AI-powered email design"
• "New: Shopify integration is live"
• "We just launched something big"

7. The Social Proof

Leverage other people's results to build credibility.

• "How Sarah grew her list to 50K subscribers"
• "This brand's welcome series converts at 12%"
• "What 500 top marketers do differently"

The Technical Details

Length

Keep subject lines under 50 characters for maximum visibility across devices. Mobile cuts off at around 35-40 characters, so front-load the important words.

Personalization

Using the subscriber's first name in the subject line can boost open rates by 10-15%. But it's not magic — a bad subject line with a name is still a bad subject line.

Emojis

One well-chosen emoji can increase open rates by drawing the eye. But research is mixed, and overuse looks spammy. Test with your audience.

Preview Text

Always write custom preview text. It's your subject line's wingman — use it to add context, create additional curiosity, or deliver a secondary hook.

How to Test and Improve

The only way to know what works for your audience is to test. Here's a simple system:

1. Write 3-5 subject line variants for every campaign

2. A/B test the top 2 with a small segment (10-20% of your list)

3. Send the winner to the rest

4. Track results in a simple spreadsheet — note which formula/approach worked

5. Review monthly to identify patterns

Over time, you'll build a playbook specific to your audience. What works for a B2B SaaS newsletter is different from what works for a fashion e-commerce brand.

Stop Overthinking, Start Testing

The biggest mistake with subject lines isn't writing bad ones — it's spending too long agonizing over the "perfect" line and never testing alternatives.

Write fast, test often, and let the data tell you what works. Tools like TopMail's A/B testing make this effortless — you write the variants, and the platform automatically sends the winner.

Your subject line is the first impression. Make it count.