How to Write Subject Lines that Boost Open Rates

The only thing standing between your well-crafted email and your subscribers is the right subject line. We'll share our guiding principles to writing effective subject lines and provide tips that will help you improve your open rates.

You've spent a lot of time crafting the perfect email. You're excited to share it with all your subscribers. There is one last step that can make or break your campaign — writing a compelling subject line.

The subject line along with your preheader text compete with hundreds of other emails in your subscriber's inbox. If you get the messaging right, they will open your email. 

Don’t let a poorly written subject line ruin your campaign before it even starts.

We’ve identified three guiding principles to help you write effective subject lines: 


  1. Personalize it.
  2. Make it relevant.
  3. Test to optimize.



How to personalize your subject lines

Email marketing is one of the most personal forms of marketing communication. The ability to target individuals allows you to personalize your messaging which improves your conversions. 

Here are a few ways you can personalize your subject lines and make a stronger connection with your readers:

Insert your reader's name into the subject line. 

When a reader sees his or her name in the subject line, something happens in their brain where they need to see what it is. This level of personalization is easy to implement and available to every MailerLite user.

Refer to your reader's location. 

People feel a connection to their hometown. When you include location-specific language in the subject line, your readers will be curious about what is happening in their area.

Highlight your reader's interests. 

If you have collected data on your users, find ways to connect with them through their interests. For example, you can segment your audience by their favorite sports team. 

By calling out something meaningful to your subscribers in the subject line, they are more likely to open the email.

Note: Personalization can generate great results, but you have to be careful NOT to use it every time you send an email. Too much will lessen the effect until the reader starts ignoring it.

Personalize sender address

You can have the most personal subject line, but if the email is sent from a strange email address, your email will end up in the trash, or even worse — marked as spam.

The first thing two things people look at in their inbox are the subject line and the sender's name. Use a familiar name. If possible, send the email from a real person. 

For example, 'Jonas from MailerLite' works well because the reader will recognize the company and the name adds a personal touch.

When an email is sent from a familiar sender, opening rates increase by as much as 28%. In a world of endless spam and email bots, personalizing your sender address breaks through the inbox clutter. 

* See More Personalization Ideas
How to personalize email marketing

How to make subject lines relevant

Sometimes personalization isn't the right approach for your campaign. If it’s not, your goal is to write subject lines that are super relevant to your target audience.

You need to clearly communicate something that the reader either really needs or wants. To be truly relevant, you need to be specific and descriptive in your copy.

Don't be tempted to use catchy phrases or clickbait to get high open rates.

Not only are readers turned off, but it also indicates that your content is not relevant enough to explain it simply.

Which headline is more descriptive?

Subject line #1 is not very descriptive and makes a big claim with nothing to support it. On the other hand, line #2 lets the reader know exactly what to expect in the email.

People have dozens of emails to filter through. Get to the point quickly!

The best subject lines make a promise and then deliver on that promise. Of course, your content must deliver on the promise, or your bounce rate will go through the roof.

What is relevance?

Email marketing that is relevant means sending the right messages to the right people. Tailor your content to your reader’s interests and desires.

Instead of blasting out an email to your entire email list, you can increase relevance by segmenting your audience into smaller groups. When you send emails to smaller portions of your list, you can get more specific based on that group's interests or needs.

* Learn More About Segmenting Your Email List
What is Email List Segmentation and Why You Need it

You can also increase relevance by implementing automation triggers, which send people emails based on their behavior. For example, when a user reads your blog, you can automatically send them an email with more content related to the blog. You can't get more relevant that!

* Learn More About Email Automation
What is Email Automation and Why You’ll Love it

7 tips to improve your subject lines

1. Consider mobile display

Over half of your subscribers are viewing emails on mobile devices. The subject line parameters change with mobile. iPhone cuts off subject lines after 35 characters but gives 140 characters of preheader. Keep your subject lines under 40 characters to ensure it's readable on every device.

2. Ask a question

People like answering questions. Questions draw the reader into the conversation as a participant. Try subject lines that pose a question to pique curiosity. Your open rates are likely to increase as people naturally want to find answers.

3. Use numbers and lists

For some reason, people love to click on emails with numbers and lists. Perhaps it's because their expectations are clearly defined or it's easier for the brain to process. Whatever the reason, numbers and lists have been proven to work.

4. Avoid looking like spam

Don't use phrases that sound too salesy or make promises you can't keep. Readers are savvy to click bait and will immediately mark your email as spam. Do your best to minimize exclamation points or CAPS. People are usually not as excited as you are about your email.

5. Leverage scarcity

Have you ever noticed how Apple sells out of their newest products forcing most to wait? Apple has mastered the scarcity principle, where the value rises when demand is greater than supply. You can use this same strategy in your subject line. Let readers know that your offer is limited or has an expiration date.

6. Experiment with emojis

Know your audience and proceed with caution. Younger demographics love emojis. If you use them appropriately, they will help improve open rates. More professionally-minded audiences might NOT respond well to emojis. 

7. Give a command

Sometimes your readers need to be told what to do. Giving them clear direction and a strong call-to-action will actually help them take action. The trick is to give a directive without being too bossy. 


Wait! Don't forget about preheaders

The preheader is your subject line's best friend. It's the first line of text that appears next to the subject line. This is especially important for mobile devices where the preheader is often more prominent than the subject line.

For example, iPhone only allows 35 characters for a subject line, but displays about 140 characters of preheader. That is a full tweet! (Well, an old tweet before twitter increased it to 280 characters).

Preheaders provide an additional opportunity to increase your open and click-through rates

Seize the opportunity to include compelling text that communicates your value proposition and motivates your readers to open the email.


Experiment & test 

If a tree falls in a forest and no one is around to hear it, does it make a sound? You spend a lot of time crafting the perfect email, but if no one opens it, they will never know what they are missing.

Take the extra time to write subject lines that will pique your reader's interest. 

  • Describe the benefits of your email. What's in it for them?
  • Keep it fresh. If something works, that doesn't mean you use it every time.
  • When in doubt, test! MailerLite's A/B Testing feature makes it easy for anyone to test subject lines.

Testing your emails is so important, we wrote a whole chapter on it.

* Learn More About Email Testing
Email Marketing A/B Testing made Simple

The subject line and preheader should work together to build anticipation of your valuable content. In our next chapter, we’ll cover everything you need to know about writing effective email content.

P.S. One more thing

We believe that the ‘from’ field is even more important than your subject line. 

You don’t care what is the subject line of the email you received from your mum, right? That’s the point. We usually open and read emails that are sent by someone we trust and know. 

Make sure your readers recognise the sender name and want to open the email. That means you should to deliver value in every single email to build your reputation.