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How to Write Email Subject Lines

Updated Oct 24, 2023

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If you’re sending marketing emails that aren’t delivering your hoped-for results, your subject lines could be to blame.

In addition to using the best email marketing software, subject lines are one of the most critical factors in an email marketing campaign’s success. Without a catchy email subject line, the likelihood of someone taking the time to open and read the message drops considerably.

Here’s a look at what makes an email marketing subject line effective and how to craft one that draws your readers’ interest. 

The importance of a catchy subject line

Leah Miranda, director of campaign operations for CM Group, said good subject lines are vital to email campaigns’ success. The subject line sets the foundation for your subscribers’ experience with the email.

“If it’s well-written, attention-grabbing, and fulfills a need, then the individual will likely open the email and interact with the content inside,” Miranda said. “If the subject line is the opposite of that, then there’s a good chance it will end up being unread or in the trash.”

Dave Charest, director of content marketing for Constant Contact, said that other than the email’s sender, subject lines are the most critical factor in the message being read.

“If an email recipient doesn’t recognize the sender, the subject line needs to work extra hard to entice that person to open it,” he said. “But if an email recipient recognizes the sender and has a good relationship with the person or business, then that person is more likely to open the email regardless of the subject line.”

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Email inboxes are filled with dozens, if not hundreds, of promotional email messages every day. This is why Len Shneyder, vice president of industry relations for Twilio SendGrid, says he can’t stress enough how important an email subject line is in grabbing the recipient’s attention. A good subject line can start the type of chain reaction businesses are hoping for when launching marketing campaigns.

“Subject lines are part of a chain of microdecisions that lead to opening the email, clicking a link in the message body, and hopefully converting the user to the brand,” Shneyder said.

Did You Know?Did you know

Along with poor subject lines, common email marketing mistakes include selling too hard, forgetting to optimize your emails for mobile devices, and avoiding customer segmentation.

How to write an effective subject line

With so much on the line, it’s crucial to put some serious thought into your subject lines. Here are the factors to consider when writing subject lines to give you a better chance of enticing recipients to open your email, click through your links, and become long-term, engaged customers.

1. Personalization boosts open rates.

Personalizing your subject lines is an excellent start when you’re trying to boost your open rates.

“By doing something as simple as adding the subscriber’s first name in the subject line, it makes the individual feel as though the email was specifically made for them,” Miranda said. “When you’re looking to advance beyond the first name, you can personalize it based on your subscriber’s interests in a certain product, topic, or service.”

Research from DMR shows that email open rates increase by 17% when the subject line is personalized, while click-through rates rise by 29.6%.

2. Length impacts a reader’s engagement.

The number of words in your subject line can impact whether or not someone decides to open the email. Charest said it’s important to have short subject lines of four to seven words.

Mobile devices have made this element especially important. While the average desktop client shows about 65 characters in a subject line, according to Miranda, mobile phones only display 30 to 50 characters. Keeping your subject line short prevents it from being cut off when read on a smartphone.


To keep your subject line concise, make it only five or six words with no more than 35 characters total.

3. Use important words first.

You don’t have a lot of time to grab the attention of someone scrolling through their inbox. With that in mind, Miranda encourages putting the most important information first to grab their attention.

“For example, if the subject line is ‘Summer clothes are 50% off,’ your subscriber doesn’t find out about the deal until the end. If you simply swap the order, then the first thing they’ll see is ‘50% off,’ and who doesn’t love a good deal?”

4. Avoid certain words.

Many words have been so overused in email subject lines that readers might decline to open the email or, worse, delete it. Many email service providers use these words to identify spam messages.

While your subject lines should indicate the value your emails offer readers, don’t oversell your products or services. “Additional income,” “be your own boss” or “no catch” are among hundreds of email spam trigger words and phrases to avoid. These words might seem unbelievable and scam-like.

5. Avoid excess punctuation.

To write effective subject lines, you can’t focus on the words alone. Charest recommends avoiding excess punctuation and symbols in subject lines. He also discourages writing your email subject line in all caps.

6. Engage in A/B testing.

Instead of guessing what makes a great subject line, you’re better off trying multiple options with A/B testing tools. This allows you to see which subject lines garner more interest.

“Subject lines are one of the easier emailing differentiators to test,” Shneyder said. “Always A/B test your email campaigns to measure what’s working and what’s not.”


Along with A/B testing, it’s important to study your email list and campaign analytics to determine the optimal time to send your messages. Check out these other email marketing tips.

7. Think about the preheader text.

In addition to the work you put into the subject line, Miranda said you need to think about the preheader text, which is the copy that follows the subject line. An effective preheader can increase your email’s open rate by 7%.

“If you have a great subject line and the preheader text says, ‘View message online,’ that sounds like a poor user experience,” Miranda said.

This text can be a quick summary of your email or a call to action. The purpose of this text is to present the most important points and give your recipients significant details of your email before they open it.

To create an effective preheader, personalize the text to your readers. Ask questions that encourage your recipients to open your message. For example, for the subject line “How to get 10 new clients,” the preheader text could ask, “Ready to reach more people?” This text can spark your subscribers’ interest in how your strategies can help them expand their business.

Benchmarks for email open rates

How do you determine if your subject lines are making enough of a difference with your open rate? One answer is looking at the average open rates for emails from businesses in your industry.

According to Campaign Monitor, emails from advertising and marketing agencies averaged an open rate of 18.5%. Wellness and fitness companies had a 21.6% average email open rate. Financial services averaged a rate of 24.8%, while media, entertainment and publishing agencies averaged a 20.8% open rate.

Negative effects of bad subject lines

The importance of a catchy subject line can’t be overstated. A good subject line can result in an engaged and long-term customer, while a bad one can lose you a customer forever.

Miranda said the subject line will make or break your email open rates. “But beyond this, it will also affect your click-through, click-to-open rate and even your unsubscribe rate. While subject lines may seem like only one small piece of the entire email marketing strategy, they hold a substantial amount of responsibility in terms of success.”

It’s important to remember that the more emails you send, the more your name and brand will become tied to your subject lines, according to Shneyder. As a result, notoriously bad subject lines have a lasting negative impact on you and your brand. They can also breed disengagement.

“For example, if I know that a company’s subject lines are misleading or overhyped, I might delete the email before reading what it’s about,” Shneyder said. “Getting your reader to click – to engage – is vital. Breed engagement with good subject lines, and you will keep your spot in the inbox.”

Bad subject lines can also draw the ire of mailbox service providers, including Gmail. Shneyder said Gmail analyzes which unopened emails a user deletes. In a move to streamline your inbox, it could send future emails from that company straight into the spam folder. 

Then, when you have an important announcement, the chances of engagement are almost zero. You will never have effective email campaigns if your messages get caught in spam filters.


You can also improve customer engagement by connecting with consumers on social media, offering help over live chat, and monitoring your web analytics.

Why you should avoid clickbait subject lines

Research shows that clickbait subject lines designed to shock readers into opening an email and those that promote prices and discounts are among the least effective.

Previous research from email deliverability firm Return Path found that while clickbait subject lines like “you won’t believe this shocking secret” are successful at garnering web traffic, they don’t provide the same results over email. 

Specifically, the phrase “secret of” in a subject line results in an 8.69% decrease in read rates compared with messages containing similar content with different subject lines. Additionally, using the word “shocking” had a 1.22% decrease in read rates.

“Marketers should always avoid clickbait subject lines, because if subscribers are over- or under-promised about what will be inside the email, they are likely to unsubscribe or, worse, report the email as spam,” Miranda said.

The research also revealed that value-based subject lines highlighting prices and discounts don’t perform as well as you might expect. Subject lines containing the keywords “discount,” “save,” “sales,” “clearance” and “free,” as well as those with dollar signs and percentages, yielded lower read rates than comparable messages with alternative subject lines. 

While you might get some initial traction with a clickbait subject line, it’s a poor strategy for building and tracking audience engagement. Businesses want to foster long-term engagement with email marketing campaigns.

“You should avoid clickbait subject lines because they only work once, maybe twice,” Charest said. “Then you lose the trust of your email subscribers, which is so important to maintain long-term.”

The research, based on the analysis of more than 9 million subject lines received by more than 2 million subscribers, revealed that a better option is to use subject lines that are benefit-based or have a sense of urgency. The study discovered that subject lines featuring superlatives like “fastest” generate 5.3% higher read rates than similar messages with different subject lines.

Urgency-based subject lines with words like “limited time,” “last chance” and “expiring” also increased open rates.

Shneyder said email marketers should consider their audience’s perspective before using a clickbait subject line. Think about your reaction to clickbait subject lines. Would you trust the sender of such an email?

“As the sender, you want the receiver to find comfort in your brand popping up in their inbox,” Shneyder said. “Be honest with your receiving party, and they will be more willing to listen, to open, and – hopefully – to engage.”

Shayna Waltower contributed to the writing and reporting in this article. Source interviews were conducted for a previous version of this article.

Chad Brooks
Staff Writer at
Chad Brooks is a writer and editor with more than 20 years of media of experience. He has been with Business News Daily and for the past decade, having written and edited content focused specifically on small businesses and entrepreneurship. Chad spearheads coverage of small business communication services, including business phone systems, video conferencing services and conference call solutions. His work has appeared on The Huffington Post,,, Live Science, IT Tech News Daily, Tech News Daily, Security News Daily and Laptop Mag. Chad's first book, How to Start a Home-Based App Development Business, was published in 2014.
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