Email subject lines dictate whether someone will click on your email or ignore it completely. In many cases, an email campaign’s success or failure hinges primarily on the quality of its subject line. But how do you write a subject line your audience can’t resist opening?

To capture the fleeting attention span of your email recipients, aim to craft a subject line that not only stands out from your competitors but invites your customers to take action. If you need a hand increasing your email open rates, then you’re in luck. In this article, we’ll discuss tips and tricks to use in creating the best email subject lines, including personalization, clarity, and thoughtful use of punctuation and emojis. Plus, we’ve rounded up five of the best email subject lines that follow best practices.

5 tips for subject lines

Crafting email subject lines that get results is both an art and a science. There are a few best practices to follow if you want to achieve higher open rates, including personalization, keeping your subject lines short for mobile compatibility, being descriptive without overdoing it, limiting punctuation to avoid spam filters, and using emojis strategically to connect with your audience.

1. Add personalization

It’s out with the sales jargon and in with personalization. With a wealth of data under our belt, customers expect us to know exactly what they want — and they don't want to see another yawn-inducing generic email subject line. Adding personalization to email subject lines can improve open rates by 22%.

Making use of merge tags to use your readers’ first names or locations in your email subject lines makes them feel valued. Out of the dozen or so emails landing in your inbox daily, the ones that are likely to catch your eye are the ones mentioning your name.

Avoid sending mass, generic emails too. By targeting your messaging—and therefore your subject lines—to different audiences with different preferences, your emails are more likely to be opened.

2. Keep it short

Do a quick search on “email subject lines” and you’ll find the topic of subject line length popping up a lot. Why? Because, unlike the other elements that make up a subject line, its length is the easiest one to measure.

Subject lines are designed to grab your reader’s attention quickly.

Not only do you want a punchy one-liner, but you’ll also find that mobile displays up to 30 characters of an email subject line, the rest will be cut off, leading to disappointing open and engagement rates.

Start prioritizing your compelling subject lines. Keep them interesting, precise, clear, and most importantly short. Make every word count and if people don’t respond to your first email, don’t give up. Send a follow-up email with a new subject line to give your email a second chance.

3. Be descriptive

Yes, we said shorter was better—but that’s not always the case. Research by Gartner found that businesses with the most email marketing success often use more detailed, descriptive subject lines, leveraging personalization and targeting.

But getting descriptive isn’t about using flowery language. It’s about making it very clear what your email contains.

“Marketers with the most data are infusing it in their subject lines by specifying the product, the user’s rewards status, location, and more,” according to Gartner. “This means longer subject lines are effective as long as they align with more sophisticated targeting.”

4. Limit punctuation

Don’t use any more than three punctuation marks per subject line, according to Mailchimp—too much punctuation can give your email the appearance of spam, particularly if you’re using special characters.

Hubspot notes that, in particular, “web servers flag emails as spam if they contain both a question mark and an exclamation mark in the subject line.”

5. Use emojis carefully

A report by Experian found that 56% of brands using emojis in their email subject lines had a higher unique open rate than text-only subject lines.

Emojis are useful for many reasons. For a start, they save space. If you want your entire subject line to fit on a mobile device and you only have 30-40 characters to play around with, adding an emoji can be the key to getting your message across without using many words.

They can also help brands to convey emotions. Given that many brands today are constantly struggling to form an emotional connection with customers, emojis may assist in bridging that gap.

It’s important not to get carried away using emojis, though. According to Mailchimp, you should only use one emoji at a time, and avoid using emojis to replace words. Plus, remember different operating systems render different versions of emojis, so it’s important to test.

Test variations of subject lines

Increase your open rates further by testing elements of your subject lines—from length to emojis—using A/B testing or AI.

Use A/B testing for subject lines

A/B testing subject lines allows you to fine-tune your messaging, ensuring it resonates with the target audience. The nuances of language, tone, and content can significantly impact your open rates.

A/B testing is simple: Create two versions of your email with different subject lines and then send them to two groups to see which performs best—most email marketing platforms have built-in A/B testing functionality.

Your test could be as simple as testing the difference between a single word, or variables like length, personalization, urgency, and curiosity—but importantly, make sure you’re only testing one element at a time otherwise you can’t be sure which difference is impacting the open rate.

Use AI to test subject lines

Millions of marketers before you have composed subject lines with corresponding open rates, generating trillions of data points. With Ortto's AI subject line writer, anyone can tap into this wealth of information to not predict the open rate of their subject line. The AI will also write recommendations on higher-performing alternatives.

The AI subject line writer was trained by Ortto engineers on billions of email subject lines and their open rates. This purposely trained neural network takes this data and accurately predicts your open rate. Plus, it will recommend some higher-performing alternatives for you to consider.

Not only will you benefit from a higher open rate on your email, but over time you'll start to learn what makes people click and the subject lines you enter into the AI will improve, along with the recommended alternatives.

Five of the best email subject lines

This short and sweet subject line from Asana gets straight to the point, and in just 22 characters makes a clear yet compelling case for why it should be opened. After all, who wants to miss a deadline?

Grammarly's subject line, "You're just a step away from your AI writing results," is a real winner for a couple of reasons. It's got a touch of excitement, emphasizing that the recipient is on the brink of getting something valuable – their AI writing results — while being clear and straightforward; there's no guesswork involved.

This subject line from Venmo is like a helpful tip from a friend, letting you know an easy new way to pay for your fast food delivery. The message is all about convenience, which resonates with all Venmo users who value simplicity in their payment options.

Buffer shows that sometimes longer is better with a detailed subject line that tells the recipient exactly why they need to open the email -to register for their live session.

Personalization is powerful. This subject line gives the recipient a good reason to open it, with a special offer on items they’ve personally been browsing.

All images from Really Good Emails.

The final word

A lot of effort goes into creating email content, from the design of the email right down to crafting the perfect call-to-action prompt. However, all this effort will go down the drain if your email remains unopened in your customer’s inbox thanks to a non-optimized subject line.