Increase Klaviyo Email Open Rates With These Email Subject Line Tips

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7 min read
by: Holly Kuldell03/12/2021

Quick Summary The art of writing an engaging email subject line is just that: an art. There’s no one perfect subject line, just like there’s no single perfect painting. However, there are plenty of techniques to improve your subject lines and important strategies to determine whether you’re making an impact.

Luckily for email marketers, judging the effectiveness of a subject line is straightforward. Unlike art, you can spot whether your subject lines are working by monitoring your open rate. To find your open rate, just divide the total number of people who opened your emails by your total number of subscribers. The higher your open rate, the more successful your e-commerce email marketing campaign is likely to be. 

While your subject line isn’t the only important factor in an email campaign, it’s still crucial. Why? Because your subject line is the first and potentially the only thing your subscribers will see. 

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If your subject line doesn’t interest readers, then they might ignore the email, delete it without opening, unsubscribe from your email list, or even report your emails as spam. That’s not great for customer retention, to say the least.

Studies show that the average office worker receives a whopping 121 emails per day, and nearly half of all email recipients decide whether to open an email based on nothing but the subject line. A good email subject line is the only tool you have to stand out from your subscribers’ crowded inboxes.

No matter what you’re working to improve in your email marketing, Klaviyo can help. Klaviyo’s email marketing tools can help you segment and target your emails better than ever before. Combined with effective subject lines, you can get attention even in the most crowded inbox.

There are a couple of email marketing strategies you can use to write more engaging subject lines, and you can divide this up by the method you’re using to build interest. Here are some of the best email subject lines and the techniques used to write them. 


People hate feeling like they might miss out on something important or interesting. This feeling is so common that it has a name: “FOMO,” or Fear Of Missing Out. Harnessing your subscriber’s FOMO is a great strategy to boost your open rate.

You can trigger FOMO by using urgency in your subject line. Terms like “one day only,” “limited time,” “last chance,” and “ends soon” are all great ways to give your emails a sense of urgency. Even if a reader might not have cared about the sale otherwise, if you make them feel like they’re about to lose out, they’re more likely to click through.

This Coldwater Creek subject line is an excellent example of instilling a sense of urgency:

Coldwater Creek Subject Line: Ends Today!

Coldwater Creek: “Ends today! 36-Hour Outlet Sale. Hurry, this is your last chance...”


People don’t like the feeling of spending money. However, people do like the feeling of saving money. The thought that they’re getting a good deal can encourage many consumers to make a purchase they wouldn’t have considered otherwise.

You can encourage people’s love of a deal and sense of frugality by mentioning a sale offer in your subject lines. Terms like “50% off,” “save,” and “free shipping” are excellent triggers for people who love a deal. 

This ModCloth subject line encourages people to buy more to save more, giving customers a push to click the email to find what products are on sale. 

ModCloth Subject Line: Sale

ModCloth: “Buy 3, get 30% off? We love to see it.”


There aren’t many people out there that will argue that laughter is bad. Most people enjoy laughing, and a funny subject line can appeal to a wide variety of subscribers. As long as your brand isn’t focused on remaining entirely serious all the time, a little humor in your headlines can boost your clickthrough rates. 

Make sure you tailor your jokes to your audience. If your brand is aimed at older demographics, making a joke about Harry Potter may not land. Plus, you only have a limited amount of space, so get clever with the room you have. The best 2021 subject lines are timely, so jokes should also avoid outdated references. 

OpenTable put out an April Fool’s campaign where they claimed they had made an app that allowed you to taste restaurant meals and menus by licking your phone. Their subject line? “Licking your phone never tasted so good!” While the app was obviously fake, the funny email got plenty of clicks from users who wanted to learn more. 

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Most people have some problems that need solving. You can make a pretty educated guess on the problems your subscribers may face if you’re using Klaviyo’s market segmentation tools to track your audience. By presenting readers with a solution to their problems in your email subject lines, you can encourage them to click through and find out what you’re offering. 

You can also bring up pain points to remind users of their problems, then imply answers. Terms that imply answers to those problems can give users hope for a solution that they’ll learn in your email. 

Sephora knows exactly the problems their customers face. A recent email subject line was “Your beauty issues, solved.” It’s short, to the point, and makes users curious to learn what solution Sephora is going to present. 


The internet can make people feel anonymous and ignored sometimes. By sending your subscribers personalized emails, you can make them feel a little more special and seen, which builds customer loyalty. 

Things you can customize include adding their first name to emails, sending them special birthday deals, or referencing their general location. Just make sure you’re being useful and not creepy!

LivingSocial is the king of personalized emails to people in a certain area. For people in the Boston metro area, they may receive an email like the following, referencing the best deals that are local to them. 

Living Social Subject Line: Localized

LivingSocial: Best of Boston: Avanti Salon & More


Sometimes, less is more. Keeping your email subject lines short will make them stand out in a long list of competing messages. 

A famously short and famously successful subject line during the 2012 presidential election was simple: “Hey.” In a field where chatty subject lines are common, the Obama campaign’s simple title caught the eye and stood out from the pack in a way that even Bloomberg Businessweek noticed. 

Obama Subject Line: Hey

Barack Obama: “Hey”

Pop Culture References

If your brand has a more casual tone, pop culture references can be a great way to grab attention and clicks. It’s important to walk the fine line between relevancy and overdone, of course. 

UncommonGoods walked the line by referencing the classic movie The Princess Bride, with the simple subject line “As You Wish.” Their slightly offbeat audience was sure to recognize the reference and feel a sense of comradery because of it.


People have a strong sense of curiosity. Adding a little sense of shock or mystery to your email subject lines can pull people in. Keep your mysterious, shocking title inoffensive, of course!

To advertise a new line of metallic clothing, menswear brand Chubbies sent an email with a simple subject line: “Hologram Shorts?!” While they explained the concept in the email, the intriguing title convinced plenty of people to click through and learn more. 

General Tips for Effective Email Subject Lines

Just because you’ve used the right subject line techniques doesn’t give you a free pass to ignore other email marketing strategies. Keep these tips in mind when you’re writing your next email campaign for better open and response rates.

  • Know your audience. Your brand has a unique audience, and you need to cater to them. A grilling accessories brand and a makeup brand can both use humor in their subject lines, but the jokes will probably be very different. 

  • Remember your brand’s tone. Lighthearted, goofy brands are much more likely to see good results with jokes and pop culture references than serious luxury brands. Remember your brand’s overall tone to keep things connected.

  • Preview it to see how it’ll look for the customer. Something that looks great in your word processor may not look the same in your email. Avex and Klaviyo Partners can use powerful tools to preview how your emails will look once they’re in your customers’ inboxes to make sure everything works correctly.

  • Make sure it’s readable on mobile devices. More than 68% of emails are viewed on a mobile device. When you’re previewing your emails, make sure they work on desktop and mobile so you don’t miss a big chunk of your audience. 

  • Use A/B testing with different versions to find the best option. When you’re first learning your audience, it helps to perform some science experiments to find out what they like. Do some A/B testing with different versions of subject lines to spot which one gets better response rates and develop the best email subject lines for your subscribers.

  • Use numbers and punctuation to stand out. In a crowded inbox, anything you can do to catch the eye can help. Punctuations, numbers, and even emojis can help you improve open rates as long as they’re relevant to your email and fit the tone of your brand. 


You can put together the world’s greatest email campaign, but it won’t matter if no one actually opens your emails. The right subject line can make all the difference. When paired with Klaviyo’s e-commerce email marketing tools, you can build a campaign that gets opened and builds customer loyalty. With a little creativity and the right techniques, you can elevate your emails to a true art form. 

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