A/B Testing Emails: Subject Lines That Drive Opens

Why Your Email Subject Line Is Your First (and Sometimes Only) Impression

You’ve spent hours crafting the perfect email—compelling copy, eye-catching design, a killer CTA. But none of it matters if your subject line doesn’t get the email opened.

With the average office worker receiving **121 emails per day**, your subject line is your one shot at standing out. That’s where A/B testing comes in. By testing different subject lines, you can pinpoint what resonates with your audience and **dramatically increase open rates**.

Let’s break down the science of A/B testing email subject lines—what works, what doesn’t, and how to turn passive scrollers into engaged readers.

How A/B Testing Email Subject Lines Works

A/B testing (or split testing) involves sending two variations of an email to a small segment of your audience to see which performs better. The winner then gets sent to the rest of your list.

What You Should Test in Email Subject Lines:

A study by Campaign Monitor found that **personalized subject lines increase open rates by 26%**, while emails with emojis see a 56% higher open rate in some industries.

5 Proven Subject Line Strategies Backed by Data

1. Keep It Short & Punchy

The best-performing subject lines are **between 30-50 characters**. Anything longer risks getting cut off on mobile.

✅ “Your VIP Access Inside”

❌ “We’re Excited to Announce Our Exclusive VIP Program for Loyal Customers Like You”

2. Spark Curiosity (Without Clickbait)

Curiosity drives opens, but misleading subject lines hurt trust.

✅ “The Secret to Doubling Your Clicks”

❌ “You Won’t Believe What Happened Next!”

3. Use Numbers & Specifics

People love specificity. Instead of vague promises, give them exact value.

✅ “5 Tools to Save 10 Hours a Week”

❌ “Ways to Be More Productive”

4. Test Personalization Tactics

First-name personalization works, but advanced tactics like location or past behavior can be even stronger.

✅ “Alex, Your Chicago Store Just Got New Arrivals”

❌ “Check Out Our New Arrivals”

5. Create Urgency (But Don’t Fake It)

False urgency leads to unsubscribes. If you say “24 hours left,” mean it.

✅ “Final Hours: Your Cart is About to Expire”

❌ “Hurry, This Deal Won’t Last!”(when it actually does)

Real-World Examples of Winning Subject Lines

• BuzzFeed: “You’ll Never Guess Which Celebrity Did This” (Curiosity)
• Dropbox: “Your Files Are Waiting” (Personal + Benefit-Driven)
• Uber: “Your Free Ride is Here” (Urgency + Reward)

These brands nail subject lines by **balancing intrigue, clarity, and value**—no gimmicks needed.

How to Run an Effective A/B Test

1. Choose One Variable – Test only one element at a time (e.g., length, emojis, personalization).
2. Split Your Audience Evenly – Send Version A to 10% and Version B to another 10%.
3. Set a Clear Metric – Decide if you’re optimizing for opens, clicks, or conversions.
4. Let Data Decide – Run the test long enough for statistical significance (usually 24-48 hours).
5. Scale the Winner – Send the best-performing version to the remaining 80%.

Tools like Mailchimp and HubSpot make A/B testing seamless.

Never Stop Testing

Consumer behavior changes constantly. What worked last year might flop today. The key? Always be testing.

Try different tones, lengths, and styles, your audience’s preferences will surprise you.

Ready to Boost Your Open Rates?

Start your next A/B test today. Pick two subject lines, send them out, and let the data guide you. The results could transform your email marketing game. Start Salesix AI free trial for change your marketing perspective. Book your free trial now.