How to write the best email subject lines to boost open rates

The only thing standing between your well-crafted email and your subscribers is a great 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 catchy email subject line for higher open rates.

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 your best email subject lines: 

  • Personalize it.
  • Make it relevant.
  • Test to optimize.

In this guide, we’ll give you our best practices and share some great email subject line examples.


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 email 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 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

Sometimes personalization isn't the right approach for your campaign. If it’s not, your goal is to write effective email subject lines that are 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 in email marketing?

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

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. Our 2020 data shows email subject lines using numbers generate a 24.97% open rate versus 23.34% without using numbers.

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. In fact, our data found that subject lines that insist on urgency perform much worse. 

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. 


We searched millions of emails to find effective email subject lines. These lines were chosen because they had exceptional open rates. While the content is specific to someone else’s newsletters, you can see what works for them and apply it to your own topics.

Catchy email subject lines
  1. I got ANOTHER sweet clean FREEBIE for you!
  2. This is not another COVID email, {$name|default:"friend"}! It's good news!
  3. [Freebie Friday] So many secrets…
  4. Welcome to your next escape
  5. I have a feeling YOU will love this!
  6. Happy Friday + Surprise Inside!?
  7. Are you an early bird?
  8. Did you invest in a financial product that wasn't great?
  9. There are literally 101 free books in this email
  10. Life happens. And so do giveaways.
Funny email subject lines (or at least trying to be)
  1. Mother nature just doesn't want to cooperate with us! ⚽
  2. I'm a stunningly bad businessperson.
  3. Join me on the magic GDPR carpet ride... (Okay, it's not magic, but I *do* have to send this email.)
  4. Cyber Week - Get your one-click finger ready
  5. It's about dang time!
  6. Sometimes you just need to vent (literally)
  7. Hold onto your seat, cross your legs, and wait for the laughs.
  8. NO, THIS ISN'T TURNING INTO A FOOD BLOG..HAHA
  9. The Good, the Bad and the...I can't think of something funny, I need a nap
  10. GDPR ≠ Gosh Darn Pretzel Rolls
Thank you email subject lines
  1. We are so Thankful for YOU
  2. Thank You for Saying YES!
  3. Dearest,{$name} Thank You for your love and support on my New Novel!
  4. Thank you for sticking with me! Check inside for a special giveaway!
  5. ★★★ Thanks for subscribing! Open to get your gift! ★★★
  6. Poll Results and Thank You Bonuses! (LOTS of goodies inside!)
  7. Thank You for Being Amazing!
  8. Here's a little thank you present for sticking with me…
  9. Thanks for signing up! **Attention required so you don't miss a thing!**
  10. Welcome! Here's a little FREEBIE to say thank you for joining the fun!
Follow-up email subject lines
  1. We Would Love to Know Your Thoughts
  2. Do you still want to receive news and updates from me?
  3. How Much Did YOU Love My Present?
  4. {$name}❤ What Did You Think Of The Wolf's Lover?
  5. We want to stay in touch - Action needed
  6. ⏳✉? When do you want to hear from me?
  7. Following up on today’s webinar
  8. Thank You & Next Steps
  9. {$name}, quick follow-up
  10. Quick follow-up regarding Cookbook, plus a few little extras!
Email subject lines for sales and promos
  1. ⚡ Sizzling Summer Releases and Hot Deals ⚡
  2. A Special Coupon Just For You!
  3. Not a newsletter but FLASH SALE!
  4. Sold out in 30 min but wait, there is hope!
  5. Alright, screw it, distro sale is 35% off and ends tonight!
  6. {$name}, It's Bonus Sale day!
  7. Sales and freebies everywhere!
  8. A DIRTY SALE, {$name|default:"friends"}!
  9. Who doesn't love a sale?
  10. Holiday sale! Yup, I've got something FREE for you!
Fear of missing out (FOMO) email subject lines
  1. Download-Binge-Repeat: Last Chance Box Sets and a Fantasy Book Deal
  2. LAST CHANCE! ⚔Get The Knight's Reward at its special launch price!
  3. Don't let this chance pass you by, {$name|default:"friends"}!
  4. LAST CHANCE! Freebies will be gone tonight!?
  5. ❤️ Share your recipe... and last chance to enter...❤️
  6. Last chance to get it {$name}
  7. ⏩ Don't Miss These Events from Wildfire Marketing!
  8. Time is flying....Don't miss out on a good deal
  9. Today is the Day! [don't miss this deal]
  10. It's decision time... Don't miss this
Curiosity subject lines
  1. I've had this in my closet for over 10 years
  2. (Mostly) Good News!!
  3. Another one bites the dust
  4. We did the thing
  5. Now, this is just getting weird…
  6. I could NOT contain my excitement...
  7. It felt like a good idea at the time…
  8. The Ten Minute Project That's SO WORTH IT
  9. Dear {$name|default:\"Reader\"}, I\'ve never done this before.
  10. So we did something crazy
Welcome email subject lines
  1. Welcome Gift!
  2. welcome, {$name|default:"new friend"}! I have exciting news inside.
  3. Welcome to Day 1 of the 7 Days of Play Email Challenge - So Why Play Anyways??
  4. ❤ Welcome To The Start Of A Beautiful Friendship ❤
  5. {$name}, welcome to Eve Silver's VIP Reader Group! Thanks for signing up.
  6. Welcome!? Here's a little FREEBIE to say thank you for joining the fun!?
  7. WELCOME AND FREE STUFF FOR YOU
  8. A Welcome Gift! My #1 Wall Street Journal Bestseller is Free Inside
  9. Hi, and welcome to my tribe! (You're going to want to open this!)
  10. Thank You For Joining The Mailing List!

Our data scientist analyzed millions of email marketing campaigns to unearth new insights about effective subject lines. Here’s what he found:

Subject line keywords that convert

These are keywords used in subject lines that tend to repeat in well-performing campaigns.

keywords subject lines convert

High-performing keywords: “update”, “bulettin”, “issue”, “breaking”, “historical”, “engaging”, “spicy”, “sweet”, “cozy”, “mystery”, “secret”, “reveal”, “members”, “freebies”, “congrats”, “winners”, “giveaway”, “survey” and names of months (September, October, etc.)

Takeaway: Subscribers like updates, but not daily! 

This chart shows open rates when using keywords associated with dates.

kw chart

Poorly-performing subject line keywords

These keywords that raise a sense of urgency tend to repeat in very poorly-performing email campaigns.

poor keywords subject lines

Subject line keywords that don't perform as well: “stock”, “ends”, “chance”, “don’t”, “left”, “miss”, “hours”, “final”, “tonight”, “fast”, “huge”, “tomorrow”, “daily”, “order” and “buy”. 

Takeaway: Subscribers don’t like feeling rushed.

Subject lines with numbers

Open rate increases when the numbers are used in the subject line for campaigns sent since 2020-01 by US and Canada accounts (24.97% Open Rate with numbers, 23.34% without numbers).

Takeaway: Numbers can increase open rate if used properly and for certain industries. See below.

  • Numbers help these industries: Open rate significantly increased (by 2% or more) for Media and Publishing, Retail, Agriculture and Food Services, Music and Musicians, Photo and Video industries when numbers were used in the subject line.
  • Numbers don't help these industries: Significantly decreased (by 2% or more) for Entertainment and Events, Software and Web App, Sports, Medical, Dental, and Healthcare, Beauty and Personal Care, Daily Deals/E-Coupons industries when numbers were used in the subject line

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 the 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.


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 email 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

Have you considered that your ‘from’ field (the sender) is even more important than your email 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 recognize the sender’s name and want to open the email. That means you need to deliver value in every single email to build your reputation.