9 Best Practices for Email Subject Lines

Despite the emergence of newer messaging channels, email continues to be an incredibly important marketing tool for brands looking to drive engagement, monetization, and longer-term customer retention. More than half of the world’s population uses email and it’s one of the channels with the highest potential return on investment (ROI), with the average ROI for email marketing reaching an impressive 42:1.

With billions of emails sent per day in the U.S. alone, however, marketers have a tough job—standing out in their customers’ crowded inboxes. The good news is a compelling subject line can make all the difference. After all, email subject lines are arguably one of the most important elements of any email marketing campaign. They’re typically the first part of the message recipients read and could ultimately be the deciding factor in determining whether an email ends up driving results or being deleted before its read.

To help your campaigns produce your desired impact, follow these best practices for email subject lines.

Email Subject Lines Do’s and Don’ts

1. Don’t be deceptive or misleading.

Don’t try to pull one over on recipients by using “RE:” to trick people into thinking your email campaign is a reply to an email they originally sent you. The same goes for referencing a nonexistent missed payment or deadline just to add urgency. These kinds of tactics can hurt your brand’s credibility and should be avoided. (Unless the email really is in reference to a missed payment or deadline, that is.)

2. Do convey a sense of urgency when you do have something timely to share.

On the flip side, urgency can actually inspire clicks and attention when you do have a campaign that’s time sensitive—for example, if you’re letting retail customers know about an upcoming flash sale or reminding registered voters that election day is approaching.

3. Don’t go over the recommended word counts and character limits for email subject lines.

As a general rule of thumb, aim for a total word count of between six to 10 words for the highest potential open rates and keep your character count to a maximum of 35 characters to ensure your subject line displays properly on mobile devices.

4. Do use personalization in your email subject lines.

Since your email subject line is the first impression your campaign will make and your first chance to connect with your audience, it’s always a good idea to personalize your subject lines whenever possible. Doing so can lead to a higher click-through rate. The personalization language Liquid makes it easy to personalize email campaigns based on a user’s first name, language, birthday, recent activity, and more.

5. Don’t worry about subject lines impacting your campaign deliverability.

Subject lines do not directly impact email deliverability except in extremely rare cases. (For example, at one point Gmail was testing out a feature where verified senders would be represented with a green check mark, and Google began blocking emails that included green check marks in the subject line, but that was an extremely short-lived and rare occurrence.)

There are no “spam trigger words'' for subject lines. No, not even “free” or “test” are off limits. Emojis are totally fine to include as well, but should be used sparingly. That doesn't mean that words don't matter—they do! If prior campaigns have generated higher spam complaints or lower engagement, then future messages including similar subject lines or phrases could be filtered as spam due to those previous negative outcomes. While you don't need to worry about spam trigger words per se, you do need to use language that aligns with your brand voice and users' expectations.

As an exercise, check your own inbox and see what’s there—chances are you’ll find there are plenty of email subject lines containing emojis or supposed spam words that have managed to get delivered to you without any issues.

6. Do test out different approaches and evaluate the impact of each.

Popular best practices for email subject lines include:

• Asking questions to pique the reader’s interest
• Being more direct
• Testing out different tones that fit your brand

Whatever you do, don’t stick with one type of subject line. Leverage A/B testing to test the effectiveness of each approach. When you’re testing, be sure to:

• Test how subject lines look on both mobile and desktop with Inbox Vision.
• Test one variable at a time: Compare shorter subject lines vs. longer ones or compare email subject lines without emojis vs. emails with emojis.

7. Don’t underestimate the importance of timing and segmentation.

While what your subject line says is important, it’s just as important to pair a well-written subject line with a send-time that’s optimized for the right recipients. Try experimenting with the timing of these messages. For instance, if you’ve just purchased a high-end, high-maintenance item, such as a smart appliance, test sending an email a few hours after your purchase, right before your delivery date, or immediately after the product is delivered.

With the Braze platform’s Intelligent Timing and real-time segmentation, you can pair winning subject lines with winning send times and segmentation to drive a more relevant and impactful customer experience.

8. Do get creative.

Get creative: Have a sense of humor, tie your messaging to a cultural moment that makes sense for your audience, include a compelling statistic, or use actionable language to grab your readers’ attention.

Struggling with writer’s block? No need to be stumped. The Braze AI Copywriting Assistant can help inspire new ideas for your email subject lines that you can tweak as you see fit. No need to open a new tool, it works alongside you as you’re using our email editor.

9. Don’t forget to ask yourself one last question before sending your campaign.

As a last check before you wrap up your email, take a look at your subject line one more time and ask yourself if it would make you want to open the email.

Ready to take your email campaigns to the next level? Check out the Braze Email Inspiration Guide.