Email subject lines are arguably your first chance to make a good impression. If you say the right words, you’re more likely to get an email open and a click if your content follows suit. A recent study by Retention Science cracks the subject line code by analyzing over 260 million delivered emails.

What they found is that subject lines with:


  • 6 to 10 words yielded the highest open rates at 21%.
  • 5 or fewer words yielded an open rate of 16% .
  • 11 to 15 words had open rates of 14%.

Incidentally, 52% of emails fell in the last category. Here’s their chart:

Subject Line Relevancy

Given that less means more, you should definitely choose your words wisely. But subject line relevance is probably more important than the number of words you use. Here are several tips to help you craft a winning subject line.

  • Don’t be afraid to ask questions. Asking a question in your subject line can pique curiosity especially if your question promises the answer to a particular problem.

  • Don’t be vague. The old bait and switch will not earn you any points with users. So, make sure your subject line directly correlates to the content inside the email.

  • Don’t be impersonal. Where appropriate, injecting a few personal details into a subject line can capture a reader’s attention. Retention Science found that using a user’s name is a safe way to go, but we suggest also trying to step up your game with details like reservation numbers, past purchases, or location information that will make your reader feel like this message was customized for them.

  • Don’t be boring. Subject lines are like headlines. Make them interesting and exciting. Again, your goals is to pique their interest.

  • Don’t make it all about you. The point of any email is to appeal to your user. Therefore, make sure the content is targeted in nature so that users don’t feel like they’re part of a batch and blast campaign.

  • Don’t use a one-and-done strategy. Testing your subject lines is a great way to find out what is most effective. You can test subject length and subject content.

To read the full Retention Science article, click here.

With more than 15 years of experience, Carly Brantz is an email deliverability and inbound marketing veteran. As the VP of Revenue Marketing at SendGrid, Carly empowers her team to transform marketing from a cost center to a revenue generator. With a key focus on funnel optimization, Carly leads the team responsible for content creation, lead nurturing, SEO/SEM, and website optimization. An accomplished speaker, Carly shares her email delivery and revenue marketing tactics as a headline speaker on SendGrid’s international roadshow as well as other Marketing conferences.