Write Compelling Email Subject Lines

By Niklas Nordlof on Monday, December 15, 2014

Open rates matter—whether you’re sending out newsletters, nurturing emails, or promotions. The key to getting customers to open your emails is the subject line. 

In 50 characters or less, you have to grab someone’s attention, and then get them to act. Unfortunately, there’s no one secret phrase or key number of exclamation marks. Writing a successful subject line is all about understanding your customer, making sure they understand you, and making it scannable.

Let’s talk more about how to do that. 

Strengthen your relationship

Before even beginning to write, consider the real reason for the email: to strengthen the relationship between you and the customer. 

You’re not trying trick customers into opening the email. You also don’t want to spam them—send them an email that they don’t want.

You want a build a rapport with your customers, so they will keep coming back to your site, recommend you to friends, and open future emails. 

How do you do that? By making sure that the email is relevant.

Make it relevant

We all get unwanted, irrelevant emails. This is the spammer approach to email, and, mathematically, it works if you send out enough emails (millions every day). But it hurts your relationship with your customers. You’ll become annoying, and your emails will be filtered to the spam folder.

Customers will only open your email if they think it’s relevant, they’ll open it.

So to make sure you’re sending out relevant emails:

  • Always opt in. Never buy email addresses. And give your customers a way to sign up for your mailing list. That way you’re only sending emails to people who want them.

  • Create multiple mailing lists. Let customers sign up for the mailing list that interests them. Maybe it’s a weekly newsletter with a digest of blog posts. Or maybe it’s a promotional list where they get sale information or alerts for new products.

  • Segment users based on data. If you set up a system for gathering analytics data, you can group customers into different mailing lists. For example, put all customers who bought jeans into your Denim mailing list, and put customers who bought wallets and belts into your Accessories mailing list.

Use the right voice

While your company may have a general tone (e.g., quirky & casual, or professional & businesslike), the voice you choose for each email should convey the information it contains.

Assuming the email is relevant, when people know what’s in an email, they’re more likely to open it. For example:

  • For promotions, you want to sound fun, casual, and engaging: Working out? Denim jorts 20% off. So show some leg! 

  • For confirmations, like with a returned product, you want a more professional and to-the-point tone: We've processed your return for Acid-Washed Denim Jorts.

  • For newsletters, your subject can also be casual, but mainly it should be informational: [Newsletter] 20oz denim jorts protect your bum while you hit the beach.

Make it specific

Vague emails don’t get opened. Most people nowadays get plenty of email, and they don’t have time to open every email. So avoid mysterious leading headlines like:

Look inside for great things!

Instead, accurately and concisely describe the email’s content:

New western-wear line from Deffell's. So cowboy up.

Of course you can also add a bit of flair to grab a customer’s attention.

Hey look at me!

Grabbing the attention of your customers isn’t about adding 15 exclamation points (This email is the best!!!!!!!!!!!!!!); although, one exclamation point, carefully placed, can be beneficial.

The best subject lines should stand out in a full inbox, and they should stand out because they’re relevant to the customer. Specifically:

  • Use keywords. The most successful way to grab customers’ attention (and make your email compelling) is to add specific keywords that resonate with them. If you’re writing for a promotional list, then make sure you’re using words like: deal, sale, savings, today only, and so on.

  • Bracket it. Using a bracketed subject (like [Webinar] or [Newsletter]) is an old technique from the early days of mailing lists. And it’s coming back. You can add your name (like [Deffell’s]), categorize an email (like [Webinar]), or preface an email series (like [Inside Deffell’s]).

  • Personalize it. Add a customer’s name to the subject line. We’ve learned that our names are relevant. So people will notice their name in a list of unread emails. For example: Hey Caleb, get 20% off jorts today through Monday.

  • Ask a question. Most subject lines are statements, so questions stand out. For example: Hey Caleb, need some jorts?

From who?

While the subject line is important, if customers don’t know who the email is from, they’ll delete it. So make sure the From line has your company name:

From: Deffell’s Pants <sales@deffellspants.com>

People put more stock in emails from people than corporations. So try sending the email from someone on your support team: 

From: Caleb at Deffell’s Pants <caleb@deffellspants.com>

Also, if your customers click Reply, they’ll get an actual person. 

Keep it short

Email providers (like Gmail) only display so many characters in the subject line. So if your subject is too long, it will get cut off. 

50 or 55 characters is the general recommendation. But if your customers are looking at your email on a cell phone, that number might be even shorter: 30 – 35 characters.

My recommendation is to say what you need to in the first 30 characters, but it’s okay to go longer.

That means you need to put the important stuff first, so when your subject line is cut off, you still get your message across.

For example:

Design your own jeans! Pick every detail, and we'll build it.

Here’s how that looks on my phone:


And on my laptop:


Use sentence case

Subject lines are an introduction to a conversation. They are a not the title of the email. So when you write a subject line, do not use title case:

Design Your Own Jeans! Pick Every Detail, And We'll Build It.

Use sentence case:

Design your own jeans! Pick every detail, and we'll build it.

Title case feels odd, and it hurts readability. On its surface, this recommendation seems minor. In fact, I almost didn’t mention it. But it’s at the heart of understanding how to write email subject lines. 

Think of the subject line as a short, introductory sentence that tells readers what to expect when they click. And if you’re using title case for your subject, then you’re probably thinking of your subject as a title and not an intro.

Don’t worry about spam filters

If you’re searching the web for information on how to write the perfect subject line, you’ll see a lot of talk about spam filters. 

Even a few years ago, email providers still filtered emails based on spammy-sounding words. So the relevant advice was to be cautious about what words you’re using. 

Well, over the years spam filters have progressed. And email providers now filter based mainly on the sender or the content of the whole email. 

So feel free to include:

  • Free 
  • Credit
  • Dollar signs ($$)
  • Exclamation points!

But avoid:

  • Emails that consist of only a link
  • Sending emails to users that did not opt in
  • Starting a phishing scheme… and other illegal activities (as if I actually had to mention this point)

Read how Gmail filters spam.

Test it

The tips in this article will help you, but in the end you’re still just guessing. So test:

  1. Pick 2 different subject lines. 

  2. Send emails with the 1st subject line to a small percent of your mailing list (5 – 10%), and send emails with the 2nd subject line to another 5 – 10%.

  3. Then check the open rates, and go with the more successful subject for the other 80 – 90% of your list. 

This type of A/B testing (as it’s commonly called) is common practice for large email campaigns. Read more about A/B testing on Wikipedia

What else?

Want more information on writing compelling subject lines? Here are a few extra credit tips:

  • Follow trends. Just steal—err… borrow—techniques from emails you like. You get email everyday. Figure out which ones stand out to you, and which ones you open.

  • Write out 10 subject lines. Write the subject line over and over again, and then pick the best one. You’ll notice that the first one you write usually won’t be best.

  • Add Gmail actions. Gmail lets developers add call-to-action buttons right in the subject line. For example, you can ask a user to review a product they purchased right from the inbox. Or add a button that sends them to a product that’s on sale. Here’s some more information about Gmail actions.

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