How To Write Better Email Subject Lines (Best Practice Guide)

Looking to write better subject lines that get your emails opened and read? You’re in the right place.

When sending marketing emails, the subject line makes the first impression on your recipients. A great subject line can be the difference between an email that gets opened and one that gets ignored.

In this post, we guide you on the best practices for email subject lines that drive engagement and boost your email marketing ROI.

Importance of email subject lines 

Email subject lines are just as important as the email content.

They play a crucial role in email marketing success, and that’s why you need to put more effort into crafting them.

Here’s why your email subject lines matter:

• They impact engagement: Email subject lines directly impact the most important metric, the email open rate. This, in turn, affects other engagement metrics such as click-through rates, response rates, conversions, and overall campaign performance.
• Creates the first impression Your subject line creates the first impression with your recipients. A strong subject line grabs attention, sparks curiosity, and encourages recipients to open your email. 
• Affects deliverability: Spammy or misleading subject lines can land your emails in the junk folder.

What makes a good email subject line?

A good subject line generally has the following characteristics:

• Short and concise: Typically under 50 characters to display fully on mobile devices.
• Is personalized: Has the recipient’s name or other tailored details on it.
• Is action-oriented (Has a CTA): Uses verbs that encourage action (e.g., Grab, Register)
• Conveys a sense of urgency and scarcity: e.g. “Only a Few Spots Left – Register Now”.
• Sparks curiosity: Create a little mystery that sparks interest (e.g., “You Won’t Believe This Offer”).

Best practice for email subject lines

Crafting compelling email subject lines is a skill that every email marketer needs to master. It’s one fail-proof way to improve email open rates and boost engagement.

Here are some of the best practices for writing effective email subject lines:

Personalize the subject line

One of the surest ways to make your email subject lines perform better is to personalize them.

Recent marketing reports show that personalizing subject lines increases open rates by 50%.

People are more likely to open an email if they feel it was written specifically for them rather than for a group of people.

How do you personalize subject lines effectively?

• Use the recipient’s first name (e.g., “Sarah, Here’s a Special Offer Just for You”).
• Reference their past interactions, such as past purchases or browsing history (e.g., “Still Thinking About That Jacket, Alex?”).
• Segment your audience based on preferences, behaviour, or demographics (age groups and gender) so you can send relevant messages to relevant groups.

Example:

Personalization goes a long way in creating a stronger connection with the recipient, increasing their chances of opening and engaging with your emails.

Write relevant email subject lines

The subject line is not just a place to grab attention, it’s also where you let the recipient know what the email is about.

Always write subject lines that are highly relevant and communicate the contents of the email. A relevant subject line ensures that people know what to expect when they open your email. 

If your email recipients find it misleading or too vague, they might ignore it or, worse, mark the email as spam.

How do you ensure your subject line is relevant?

• Ensure it aligns with the content in the email body
• Highlight the main benefit the recipient will get from opening the email. Make them know ‘What’s In It For Me (WIIFM).’
• Avoid misleading or clickbait-style phrases that may damage trust (e.g “You Won’t Believe This!”)

When you set clear expectations in the subject line, you increase the chances of engagement and reduce unsubscribes.

Keep it short and sweet

The best-performing email subject lines are always short and straight to the point.

With people receiving dozens of emails daily, long subject lines can easily get ignored. Besides, too wordy subject lines may be cut off, especially on mobile devices.

Aim to write short subject lines that are not more than 50 characters and between 6-8 words.

Remember to make it stand out by placing the most important words at the beginning.

Examples:

“Final Hours: 50% Off Sale Ends Tonight.”

This subject line is short and sweet, likely to be opened.

“This Is Your Last Chance to Take Advantage of Our Limited-Time 50% Discount Before It’s Gone Forever.”

This is too long and overwhelming, likely to be ignored.

Include a call-to-action (CTA)

Effective email subject lines have powerful action words that encourage recipients to take action. 

Whether you want them to read an article, shop a sale, download a resource or register for an event, a clear Call-to-Action (CTA) can significantly boost engagement.

Action-oriented words help to highlight what the recipient will benefit from opening the email.

Examples of CTAs that make your subject lines perform better include:

• Get
• Claim
• Shop
• Join
• Grab
• Check
• Register
• Download

These action words create a sense of excitement or exclusivity to entice your recipients to take action.

Create a sense of urgency

People are more likely to take immediate action if they feel like they might miss out on something valuable.

Use your subject lines as an opportunity to create a sense of urgency to encourage quick decision-making.

For instance, use time-sensitive words like “Hurry,” “Limited Time,” “Final Chance,” or “Offer Ends Tonight.”

Example:

Instead of saying “Big Sale Happening Now,” create a sense of urgency by saying “Only 2 Hours Left! Claim Your 30% Discount Now.”

This will help to prevent recipients from postponing their response and increase conversions.

However, be careful not to use urgency too often, as it can lose its impact over time. Also ensure that whenever you use it, it’s authentic to maintain trust with your audience.

Make it sound exclusive

Another effective way to improve your subject lines is to make people feel special.

Make the content sound exclusive so the recipient can feel like they’re getting access to something others aren’t.

You can do this by using words like:

• Exclusive
• Private invite
• For VIPs only
• Members-only

You can then offer early access to new products, sales, special discounts, or other exclusive content.

When your subject line suggests limited access or VIP treatment, recipients become curious and are more likely to open the email.

Example:

“Exclusive for You: 20% Off Before Everyone Else!”

Use numbers

Numbers make subject lines more specific, digestible, and eye-catching. 

They set clear expectations for the value the reader will get when they open the email. Numbers also make subject lines stand out visually among many text-based subject lines.

For instance, instead of vaguely saying ‘How to Save Money on Travel,’  a more compelling subject line would say, ‘5 Ways to Save Money on Your Next Trip.”

Here’s a live example from my inbox:

Using numbers makes your content seem structured and easy to consume (e.g., listicles). They make great subject lines that are more compelling for recipients to click.

Add preview text

While not part of the subject line, preview texts (or preheader text) complement subject lines and increase email open rates.

Preview text is the short snippet of text that appears next to or below the subject line in inboxes.

This extra space often provides an opportunity to expand on the subject line and entice recipients to open the email.

Here’s how to add an effective preview text:

• Expand on the subject line without repeating it
• Provide a clear benefit or tease what’s inside the email
• Keep it short and engaging, ideally under 100 characters

Subject Line: “Your VIP Discount Expires Tonight!”
Preview Text: “Get 30% off before midnight—this deal won’t be back soon!”

Start adding preview text strategically to motivate readers to open your email and increase open rates.

Ask a compelling question

Some of the best-performing email subject lines are those that ask compelling questions.

Questions naturally spark curiosity and encourage recipients to think about the answer. This makes them more likely to open the email.

When using question-based subject lines, always ensure they are relevant, engaging, and thought-provoking.

Use open-ended questions that spark curiosity or address a common pain point or challenge.

Here’s an example of a question-based subject line from my inbox:

Questions tend to engage the reader mentally, making them more likely to open and explore your email.

Use emojis

Emojis add a visual element that makes the subject line unique and outstanding in a crowded inbox.

When writing email subject lines, you can make them visually appealing by adding emojis that match the tone and email content.

For better visibility, place them at the beginning or end of the subject line.

Here’s an example of a subject line with an emoji, straight from my inbox:

However, be careful not to overuse emojis as they can overpower your message and make your email look spammy—one or two is always enough.

Also, ensure the emojis you use are responsive (display properly across different devices and email clients)

Conduct A/B tests

Email subject lines that work for one audience might not work for another.

That’s why most email service providers offer tools for conducting A/B tests.

A/B testing (or split testing) allows you to test different email subject lines to see which ones perform better.

When running A/B tests, it’s always advisable to test one element at a time (e.g., personalization vs. no personalization, numbers vs. no numbers).

Send different versions of the subject line to small sample groups and find the one that performs best in terms of open rates, click-through rates, and conversions.

You can then roll out the best-performing one to your entire list.

Example of an A/B Test:

Subject Line A: “Get Your Exclusive Discount Today”

Subject Line B: “Limited-Time Deal: Save 25% Now”

Consistently testing and refining your subject lines can help you improve engagement and inform data-driven decisions for future campaigns.

Common mistakes to avoid in email subject lines

Now that you know the best practices for writing better email subject lines, can we discuss some common mistakes to avoid in the process?

Here are some of the most common subject line mistakes that can hurt your open rates and credibility:

Misleading the reader

Avoid writing email subject lines that overpromise or trick recipients into opening the email.

If your email doesn’t deliver what the subject line promises, recipients may lose trust in your brand. They may end up frustrated and are likely to unsubscribe from your list.

Here’s an example of a misleading subject line from my spam folder:

Guess how I would have felt if I opened the email and found that there was no $100 for me? Deceived!

Another example: “Get a Free iPhone Today!” 

This is misleading if the offer is just a discount and not a free giveaway as implied in the subject.

It’s therefore good to always ensure your subject lines are honest, transparent, and accurately reflect the email content to avoid spam filters.

Using spam words

Another mistake to avoid in email subject lines is using certain words and phrases that trigger spam filters.

Email subject lines with spam words could land your emails in the junk folder. They can reduce your deliverability and make your emails seem untrustworthy.

Examples of email subject line keywords that trigger spam filters include:  

• “Free” 
• “Cash Bonus” 
• “Guaranteed” 
• “Winner” 
• “Limited Time Offer” 

Excessive use of dollar signs ($$$) and urgent phrases like “Act Now!!!” can also get your emails flagged as spam.

Example of a spammy subject line: “Free!!! Limited-time Cash Offer!!!”

Consider running your email subject lines through a spam checker tool before sending your emails just to be sure.

Using ALL CAPS and multiple exclamation marks

Email subject lines with all capital letters or multiple exclamation marks can also trigger spam filters. Besides, they look unprofessional and may turn recipients away.

A subject line like “ACT NOW!!!! DON’T MISS THIS LIMITED-TIME DEAL!!!!” is likely to end up in the junk.

To avoid this, always use the title case or sentence case instead of ALL CAPS.

Also, limit the exclamation marks to one at most if necessary.

Using a question and exclamation mark subsequently

Combining a question mark and an exclamation mark in your subject line can make it look informal or overly dramatic.

The email ends up looking unprofessional, which can reduce your credibility.

 Example: “You Won’t Believe This Amazing Deal?!”

Here, the recipient can’t figure out whether the subject line is a question or a statement. They feel confused and may end up not opening the email.

To avoid falling into this trap, always stick to either a question or an exclamation, but not both.

If you’re using a question, ensure it’s engaging and relevant to your email content.

If it’s a statement of urgency or an element of surprise, stick to one exclamation mark only!

Writing too-long email subject lines

Finally, avoid writing too-long subject lines.

Long email subject lines may end up getting cut off on mobile devices, reducing their effectiveness. If your key message isn’t fully visible, recipients may not open or engage with your email.

Example of a too-long subject line: “Hey Tina, You Won’t Believe the Insane Deal We Have for You Right Now – Act Fast!”

If the recipient views the email on their mobile phone, they may not read the whole message, and will probably ignore your email.

To avoid writing too long subject lines, always keep them under 50 characters. Remember to put the most important words at the beginning to convince the recipient faster.

Example of a concise subject line:  “Flash Sale: 40% Off Ends Tonight”

How to conduct A/B tests for email subject lines (Using MailerLite)

Are you struggling to find email subject lines that perform best for your marketing campaigns? The best place to start is to conduct an A/B test.

Here’s a guide on how to conduct A/B tests on different subject lines using MailerLite’s A/B testing tool:

Step 1: Define your goal

Start by defining what you want to achieve with the test.

The primary goal of A/B testing email subject lines is usually to increase open rates. However, you can also aim to improve click-through rates (CTR) or conversions.

Step 2: Select your subject line variations

Once you’ve logged in to your MailerLite dashboard, go to ‘Campaigns’ and choose A/B Split Campaign to start creating your test.

Select ‘Email Subject’ and create two versions of your subject line (Subject A and Subject B).

Test only one element at a time to make it easier to track the results (e.g., length, numbers personalization, urgency).

For instance, when testing numbers, you can test these two email subject lines:

A: “3 ways to boost your productivity”

B: “Do you want to boost your productivity?”

Step 3: Choose your test audience

Next, select a portion of your email list to receive the test emails. A common approach is to use 10-20% of your audience and split evenly between options A and B.

Step 4: Send the emails and measure performance

Send Version A email to half of the test audience and Version B to the other half and track key metrics such as open rate and click-through rate.

The version with the highest open rate is usually the winner.

However, if the difference is minor, you may need to test additional variations.

Once you have a winning subject line, use it to send the email to the rest of your audience. Apply the insights to future campaigns and continue A/B testing and fine-tuning regularly.

15 examples of catchy email subject lines

Here are 15 catchy email subject lines you can emulate to boost your email open rates:

Intriguing subject lines that raise curiosity:

1.  “You Won’t Believe What We Have for You!”
2.  “This Secret Will Change How You Run Your Business”

Email subject lines with urgency & FOMO (Fear of Missing Out):

3. “Only a Few Spots Left – Claim Yours Now!”
4.  “Ends Tonight! Your Last Chance for 25% Discount!”

Personalized email subject lines:

5. “Mary, This Exclusive Deal is Just for You!”
6. “Hey Kate, We Have a Surprise for You!”

Email subject lines with numbers & lists:

7. “3 Simple Ways to Boost Your Sales Today”
8. “7 Insider Tips for Growing Your Instagram Following!”

Question-based email subject lines:

9. “Struggling with Writer’s Block? Here’s the Fix!”
10. “What If You Could Make $100 in 24 Hours?”

Email subject lines with emojis:

11.  “Ready to Take Your [Skill/Product] to the Next Level?” 🚀
12.  “Big News! Something Special is Waiting for You” 🎉

Subject lines with a CTA (Call-to-Action):

13. “Claim Your 20% Discount – Click to Unlock”
14. “Sign Up Now & Get Your Free Guide!”

Subject lines with preview text:

15. “Flash Sale Ends Soon! – Get 50% Off Today.” (Preview: “Don’t miss out on this limited-time offer”)

Best practice for email subject lines: FAQs

What’s the best practice for email subject lines?

The best practice for email subject lines is to keep them clear, concise, and relevant to the email content. They should use action-oriented language to encourage readers to take action. Personalize them with first names or dynamic content when possible and avoid spammy words like “FREE” to escape spam filters.

How do you write a catchy email subject line?

To write catchy subject lines, use words that create curiosity or a sense of urgency like “Limited time offer”. Add numbers or lists and complement them with an emoji to attract the recipient’s attention. Also, keep the subject line short and sweet while highlighting the benefits.

What email subject lines get the most opens?

The email subject lines that get the most opens are those personalized with the recipient’s name. Question-based subject lines also report high open rates as well as FOMO-driven lines. Additionally, storytelling teasers like “How We Grew Our Email List by 300%” also tend to attract high open rates.

What’s the best practice for the length of an email subject line?

The best practice for the length of an email subject line is to keep it under 50 characters for better readability on mobile. In terms of words, the ideal length is between 6 to 8 words. 

Final thoughts

Writing better email subject lines is crucial for improving open rates and the overall performance of your email marketing campaigns. Now that you know the best practice for email subject lines, you can start crafting subject lines that capture attention and drive more engagement.

Remember, the rules keep changing with audience needs and so, it’s good to continuously test, analyze, and refine your approach to stay on top of the game.

Relevant and compelling emails are the surest way to turn subscribers into engaged readers—and ultimately, loyal customers!