What Do Email Marketers Need to Know About Subject Line Optimization?

December 2, 2019 | 3 minute read
Text Size 100%:

Your subject line has the greatest impact on the success of your email campaigns. If no one opens your message, no one will click on your call to action, read your content, or engage with your brand in a meaningful way. Worse, if you continue to send emails with bland subjects, your future communications could end up in spam folders.

According to research from Invesp, 69% of recipients mark emails as spam based on nothing but the subject line, while 47% of recipients open emails based on subject line alone. First impressions count for a lot. Make a bad entrance, and you may not get another chance.

With that in mind, here are a few best practices to optimize your email subject lines:

0. Personalize the subject line

Step zero should go without saying: While you don’t need to personalize every email, personalization makes a huge difference in your success rates. Marketing Dive reports that personalized subject lines increase email open rates by 50%. 

Names help, but you can do better when it comes to personalized introductions. Consider sending emails to celebrate birthdays, highlight personal interests or past activities, or point out location-specific promotions and sales. This underscores the fact that the recipient is more than just a name to you — literally.

1. Appeal to an actionable emotion

Urgency, curiosity, and even anger inspire people to act. Think about the emotional appeal of your subject lines; if you don’t have any, try infusing a little pizzazz into an otherwise bland appeal. 

To indicate urgency, include language like “Flash Sale” or “Today-Only Specials.” Avoid spammy language or clichés, like “Act Now!” or “Limited-Time Offer.” Anger works well for companies with social causes (e.g., “The Amazon is burning, and you can help stop it.”). Whatever emotion you choose, make sure you offer a clear solution to the feeling you encourage. Otherwise, recipients may resent you for riling them up over nothing.

2. A/B test different subject lines with similar audiences

Email marketers today act as part-time scientists, which means treating experiments with all the scientific rigor they deserve. A/B test a variety of features in your emails, subject lines included, but only test one thing at a time. That way, you’ll know for sure whether your test variable triggered any performance changes.

Try to convey the same type of information in a different way. You can’t compare an email promoting a sale to another email inviting people to join your loyalty program. Adjust the language, not the intent, to see how each version performs.

3. Be as specific as you are brief

People like specifics. A subject line like “We have a surprise for you….” might inspire curiosity, but it doesn’t do enough to promise a reward for a click. Something like “Say hello to our newest upgrades!” tells readers exactly what to expect while inspiring the same curiosity.

Never mismatch your subject line with the content of your email. Your audience won’t respond kindly if you promise a sale, then boast about your already low non-sale prices in the body of the email. Just as no good newspaper reporter buries the lede in a front-page story, put the most relevant information in your subject line and get to the matter quickly in the body.

4. Subvert expectations, but don’t betray your brand

Silly brands can say serious things when the time calls for it, but serious brands should exercise caution before getting flippant with subject lines. Customers of an elite wealth advisory firm in New York may not respond well to “Howdy-Ho, How’s Your Portfolio?” — even if clients in another region or tax bracket might love it.

Even if you like something personally, remember that your prospects and customers get the final say on whether a line works. If you haven’t tried something outside the norm before, do an A/B test on a random audience segment. Compare the results to those from a more buttoned-up version of the line.

Whether you send multiple emails per day or one per month, nothing dictates the success or failure of your campaign like your subject line. Marketing automation tools can help you get closer to the perfect introduction, but you’ll always need newer, more interesting subject lines to keep your audience interested. Try new things, conduct rigorous tests, and keep your customers in mind as you concoct your next perfect phrase.


You should test different subject lines to see which garners better results. You should also factor mobile into your email marketing strategy and test to see how you can optimize to better connect and engage with your audience. Find out how with “Measure Up: Mobile Testing.”

See the guide.



Serenity Gibbons

Serenity Gibbons is a former assistant editor at the Wall Street Journal and a New York University alumna living in California. She is the local unit lead for NAACP in Northern California with a mission is to ensure the political, educational, social and economic equality of rights of all persons and to eliminate race-based discrimination. She enjoys writing and interviewing people who are making a difference in the world.

Previous Post

An Extended Team: How 90octane and Oracle Marketing Cloud Work Together to Produce Content in a Mobile World

Michael McNichols | 4 min read

Next Post

In the Age of Spotify, Why Does Radio Still Exist? Because People Love Discovery In Their Diets!

James Glover | 4 min read