What We Learned Analyzing 7.5+ Billion Email Subject Lines

Illustrations of graphs and A/B testing results related to email subject lines
Published on
Jan 29, 2024
Written by
Jacob Hansen
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Spoiler: The strategies that can make or break your campaign email performance don’t apply to your triggered emails.

A subject line has a single job: Getting as many subscribers as possible to open your email. Focusing on increasing opens will help you identify the most impactful subject line variations for your brand. Plus, a great subject line will improve your email deliverability. After all—if your email doesn’t land in your subscribers’ primary inbox, they’re not going to hear what you have to say. 

We analyzed over 7.5 billion email subject lines to break down the components that can take them from good to great. But remember, a great subject line is a lot like The Beatles: Just as John, Paul, George, and Ringo combined their talents to create greatness, a high-performing subject line is the result of great synergy between the individual components. 

Triggered email subject line best practices 

When crafting subject lines for triggered emails, such as welcome series or abandoned cart reminders, keep these best practices in mind.

  • Personalized subject lines outperform those without personalization: Because these emails are triggered by shopper behaviors, including the shopper’s name or product name feels natural and can encourage action. 
  • Product names are the most powerful personalization macro, followed by shoppers’ first names: Adding the name of the product a shopper browsed or left in their cart will help you jog shoppers’ memories and bring them back to your site. And adding their first name to your welcome series can add a personal touch. You don’t want to add their full name to your subject line, though. It’s the lowest performer because it’ll push the majority of your subject out of the preview. 
  • Subject lines that include “you” or “your” perform better than those that don’t: This goes back to the behavior that triggered the email. “Your cart”  makes sense for cart-abandonment journeys—you want to be specific about what action a shopper should take.
  • Triggered email subject lines without emojis perform better than those with emojis: Keep your subject line focused on the behavior/action you want to take. These are top-of-mind reminders, not necessarily brand-building moments. 
  • Medium-length subject lines (between 25-35 characters) drive the most opens, followed by short ones (fewer than 25 characters). Medium-length subject lines are to-the-point, but give shoppers enough context to inspire them to click “open.” Plus, they won’t get cut off in previews. 

Campaign email subject line best practices 

Keep these best practices in your back pocket as you draft subject lines for your campaign emails, such as sales announcements and product launches: 

  • Subject lines that don’t include personalization macros outperform those that do: Shoppers expect campaign emails to share new products, sales, and branded content—personalization in your subject line will feel out of place, and wastes precious character count. Instead, lean into personalization in the body of your email to ensure customers receive relevant recommendations. 
  • Email subject lines that don’t include “you” or “your” perform better than those that do: Because campaign messages aren’t event-based and are targeted to a broader audience, “you” and “your” won’t feel quite as relevant to what you’re saying. 
  • Subject lines without emojis outperform those with them: Subject lines have limited (and precious) space. Emojis add to your subject line’s length without providing more information. Plus, emojis can mean different things to different people, muddying your message in such a short space.
  • Short subject lines (fewer than 25 characters) drive the most opens, followed by medium-length ones (between 25-35 characters): Campaign emails should be short, sweet, and straight to the point. Since it’s not a behavioral message, subscribers don’t need as much context or warming up. Instead, jump right into the value of the message. 

In research done in partnership with Forrester, we found that brands can achieve $2.2M of profits from triggered and campaign email by year 3.

Use these insights as a guide to crafting top-performing subject lines. But remember, your audience will have their own unique preferences. A/B testing will help you discover what works best for your brand, and each of your individual segments. Just keep in mind that when A/B testing subject line performance, you have to be intentional about creating identical splits. You should only change a single variable, such as including a product name versus not, without changing any other copy. Doing so will help you isolate the variables that make the most impact on your performance.  

Ready to grow and optimize the rest of your email program? Check out these resources: 

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