Email subject lines: a comprehensive guide

The number of email users is growing worldwide. In 2019, 293.6 billion emails were exchanged every day. With the highest ROI, emails are among the best marketing channels across industries, and subject lines are the welcome mats to your emails. If they’re creative and pique your reader’s curiosity, the recipient will open your email. If they’re not creative, relevant, or thought-out, your email will likely head to the spam folder or the bin. 

Subject lines can make or break your email marketing campaigns, and they’re well worth your time and effort. We have created this comprehensive guide on the email subject lines, their importance, learning how to write subject lines, and a lot more.

What are email subject lines? 

Subject lines are the first text-preview that recipients see along with the brand/company name, as soon as an email lands in their inbox. It gets your subscribers to open your emails, and improve email metrics. You’ve spent so much time creating beautiful emails with excellent copies, but that’s only worth the effort if your subscriber opens the email. 

Writing clear, concise, and catchy subject lines is crucial for the success of your emails. Your subscriber’s inbox is most likely filled with hundreds of marketing emails from different brands competing for attention, and unless your customers love you, your subject line is the one way to stand out.

Importance of subject lines

Since they’re the first thing your subscribers see, they must grab their attention instantly. The importance of subject lines is often overlooked, and most marketers leave it to the last minute. Believe it or not, not only do subject lines affect your click-through rates, but it also impacts your emails’ deliverability. If your subject line is unimpressive or looks like spam, subscribers will delete your emails without opening it, and your domain authority will get affected.

It’s crucial to intrigue your customers with the subject line and sustains their curiosity when they open your email. The subject line motivates customers to open your email, so test different strategies and decide what works best for your brand.

Basic guidelines for writing email subject lines

While we cover some details in length, here’s a quick look at the essential tips you need to keep in mind while crafting your email subject lines.

  • Be clear about what you want to convey through the subject line. 

  • Keep it short and sweet, so that the subject line doesn’t get cut off. Keep it within 50 characters. 

  • Learn about your subscribers’language and ensure the email and subject line are in their language.

  • Segment your subscribers and filter your email lists. Keep your subject lines location-specific.

  • Personalize the subject lines to intrigue recipients to open the email. 

  • A/B test your subject lines to see what works for your audience.

  • Don’t use special characters like @, #, *, !, etc. Service providers might read it as spam. 

  • Avoid writing in capitals. It intimidates the recipient. 

  • Don’t write clickbait subject lines.  It makes your domain untrustworthy. 

  • Don’t use promotional language like ‘Buy now’ or ‘Free.’ Servers might consider the email spammy.

How to write good email subject lines? 

According to Invespcro, 47% of recipients' email open rate depends entirely on the subject line. A lousy subject line can confuse your subscribers, put you in the spam list, get unsubscribed, or damage your email delivery rate. Let’s look at the makers of a great and compelling subject line:

Keep it short

With an increasing number of people viewing their emails on mobile devices, it’s essential to keep your subject lines short. If your subject line is more than 50-60 characters, your message will get cut midway. It’s a real task, but try to write a copy that creates intrigue and understanding.

For example, if you’re sending an abandoned cart email or other transactional emails, subject lines like “Your cart misses you” or “Complete your order” are better than “We noticed you left something in your cart, come back and complete the transaction.” The former is much easier on the eyes and gives the reader the information they need. Moreover, having anything over 5-6 words makes little sense because it defeats the purpose of creating curiosity.

Have a familiar sender name

If a known person sends the email, it can positively impact the email open rate. When you send emails with a personal name and email ID, it makes you more human and helps establish a personal connection with the subscriber. In a world where technology is evolving rapidly, humanize your emails as much as possible. For example, a welcome email sent by a familiar sender’s name would nudge opens.

Never use the no-reply sender name

While you’re trying to be as personal as possible, you must pay attention to your email ID. If your email ID says ‘’, then it defeats the purpose of having a sender name. Emails that people cannot reply to create a disconnect. Brands use the ‘no-reply’ email to avoid receiving delivery failure or email bounces that could choke their mailbox. This method might seem practical but does more damage than good to your email marketing campaigns.

Segment your subscribers

While crafting your emails, it’s essential to remember that every subscriber is on a different customer journey. Segment your subscribers based on demographics, geography, interests, historical purchases, website behavior, etc., and create email lists that are ready to engage.

Sending an email blast that is irrelevant for most people on your list can push subscribers away from your brand. They could potentially unsubscribe or mark your emails as spam without even opening them. By personalizing your emails to cater to specific segments, you have a better chance of improving your email deliverability and email metrics

Give them a sneak peek to your email

The email subject line is like a preview of your email’s content. Giving subscribers a peek into your email and creating curiosity is one of the best ways to encourage opens. For example, if your email is about a sale that ends today, your subject line could say “Ends today: Get 20% off”. 

Sending time relevant emails with the right subject line can impact your emails’ open and click-through rate.

Don’t make any false promises 

Deliver the incentive you’ve promised your customers in the subject line. If you use click-bait subject lines to have your email opened, it can be misleading customer experience. If you’re committing to giving them a discount on the subject line, make sure the email gives them the instructions. Many websites use lead magnets to increase their subscriber base. If an ebook is promised in the lead magnet, ensure you deliver that incentive. If you don’t live up to the promises you make, customers will not trust you again.

Make  your subscribers feel valued

Everyone likes to feel valued and important, and this holds for customers as well. When you segment your subscribers, you can understand how they think and anticipate their needs. When your emails make the subscribers feel valued, it creates a sense of exclusivity, and they feel important. Encouraging emails to nudge subscribers into using the product more can be a deal-breaker. Adding personalized information makes them feel special.

Create a sense of urgency

Another way to increase your email open rates is by creating a sense of urgency. You could either put a countdown (5 days left), or it could be a personalized discount you’re offering to subscribers who abandoned their cart via a transactional email. Some of these subject lines could be “Hurry! Your special coupon expires in 24 hours,” or “Your favorite pieces are selling out.”

Be more conversational. Ask a question

This is an excellent way to draw subscribers’ attention and have them open the email to get answers. A subject line with a question works best when you’ve segmented your customers and ask them questions they might be interested in.

Get creative - make it fun and punny 

Humour is a great way to connect with your subscribers, because who doesn’t like a good pun? It perks up your subscriber’s mood and puts them in an open mindset to view your emails. Don’t be afraid of letting a little joke or pun slip into your subject lines and make your subscribers smile.

Use engaging preview text

A preview text is the small bit of text that’s displayed next to your subject line. It provides a little more information and context to your email without repeating what’s in the subject line. You can use the preview text to display information that subscribers might find useful. For example, if you’re sending your subscribers a shipping information email, you could use the preview text option to display their tracking details. If you’re giving your subscribers a special discount code, you could display the code in the preview text. This makes accessing essential information a lot easier for your subscribers.

Experiment and A/B test

Learning what kind of subject lines work for your subscribers come through experimenting and A/B testing. Understanding your audience, their interests, and behavior is one aspect of experimenting while sitting down and writing what works is another. The more emails you send, the better you understand your subscribers. Maybe emojis in subject lines boost your email open rates, or personalization works well. You gain an analytical understanding of the language and content your customers are likely to respond to.

Best practices for email subject lines 

The success of email subject lines depends on six critical factors. Ensure that you consider these while crafting the perfect subject line. 

1. Urgency

Creating a sense of urgency in your subject line appeals to a subscriber’s fear of missing out on deals and offers. The feeling of scarcity will likely compel subscribers to open your email and make a purchase. We recommend limiting the usage of these urgency emails to make sure people don’t get frustrated with your brand pushing them with words like “Hurry,” “Order NOW,” or “Act Fast.” It can make them anxious, and if you use it too often, they might not trust you for long.

2. Curiosity

Curiosity is the most powerful tool marketers can tap into.  Your subject lines need not always give away everything about your content. An exciting question that leaves them feeling curious is a great way to increase your open rates. A little mystery, or even “The secret sauce to great email marketing,” can pique their interest and ensure they open the email to know more about it.

3. Offers

Marketers often use offers as a fail-proof method to have subscribers open the emails. By including the offer in your subject line, you tempt customers to not only open the email but maybe even act upon your CTA.

4. Relevance and timing

Be timely and relevant in your emails and subject lines. Catering to your subscribers’ interests is the only way you can get them interested in your brand. Remember, you need them, not the other way around. Timing is everything when it comes to sending your subscriber’s seasonal offers, welcome emails, and abandoned cart emails. Provide them with great timely content relevant to their situation or season, and you’ll have a better chance of piquing their interests.

5. Personalize

Brands that segment, target, and personalize their emails generate 58% of all revenue. The stats for personalization benefits are great, and leave you with no doubt whether it’s an effective strategy. The question is, how do you personalize without making customers feel like you’re invading their privacy? Most customers are okay with brands using their name and past purchase details to predict what they might like more. Netflix and YouTube rely on these fundamental personalization techniques in their subject lines to increase their open rates and click-through rates.

6. Social proof

If you have a celebrity endorsing your brand, include their names on the subject line. The process of using social proof in your subject line is to reassure customers that you’re a trustworthy brand. This has a psychological impact on your subscribers because their choices are now validated. Incorporating testimonials, known-names, brands, etc. in your subject line can significantly boost the way subscribers perceive your brand.


While you spend time and effort to create brilliant email content, don’t forget to focus on subject lines. Creating great content is of little use if you can’t get your subscribers to open your email. Try different methods and monitor what works best for your subscribers. Using an email automation software will take all the problems away, and automate your email sending process.