Your Guide to Writing the World’s Best Email Subject Lines

Before it hit shelves, F. Scott Fitzgerald’s The Great Gatsby was almost titled The High-Bouncing Lover. Doesn’t have the same ring to it, huh? Writing your email subject line is a lot like choosing a book title: You have to get it right, or people may never open it — no matter how fantastic the content is inside. In fact, 35% of email recipients admit to opening email based on the subject line alone, according to research from Online Marketing Summit. So how do you write the can’t-wait-to-open subject line, and not the straight-to-trash-folder version? While there’s no single formula for an ideal email subject line, the following 7 battle-tested guidelines will get you pretty close to perfect. They can help you make your messages more appealing to your subscribers. Apply them to your email subject lines, and you could be the next Fitzgerald of the inbox. (Looking for an email service provider that lands you in the inbox — and not the spam folder? Try a 30-day free trial of AWeber. We have 20 years of industry-leading deliverability!)

Email subject line rule #1: advanced personalization

The following emails arrived in my inbox during a 24-hour window.

Expedia.ie: "Marijana - (1) new message: We owe you flight deals under 150 from your home airport"
Eventbrite Picks: "Marijana's Weekly Event Guide"
Just Eat Ireland 2: "Marijana, fancy finding a new flavour?"
Collision: "Time is running out, Marijana⌛"
parkrun Ireland News: "Marijana, your weekly dose of parkrun positivity!"
mytaxi: "Marijana, upgrade your profile to a business account!"

Did any of them make me feel special? Not particularly. Variations of “Hello {!firstname_fix}” have become the norm in email marketing, not the outlier. Because of that, it’s losing its effectiveness. You can still use name personalization, but you also want to think about going a step further. At AWeber, we recommend segmenting your audience and sending each segment tailored messages with unique subject lines. “You can craft an open-worthy email by appealing to an individual’s self interests. People enjoy emails relevant to their wants and needs,” says Shayla Price, a B2B marketer who has launched email strategies for businesses like Leadpages and Shopify Plus. Here are some ways to do just that:

Ask questions on your sign up form. Then use that information in your email subject lines. For example, if you write a fashion blog, you can ask your subscriber for his or her favorite color when they sign up to your mailing list. Then, you can send them emails based off their color choice — like “15 gorgeous [color] dresses under $50.”
Send location-based emails. Traveling to a conference? Speaking at an event? Meet up with your subscribers in different cities. “We’re in [city] next week! See you there?”
Retarget subscribers. Did a subscriber abandon a product in his or her shopping cart? You could send an email like “Forget something? Here’s a 20% off coupon!” Or did a subscriber not follow through on an action, like registering for your webinar or workshop? Use that info to tailor their next message. “Only 12 hours to sign up for [event]!”

Email subject line rule #2: directness

Skip the wit, wordplay, humor, rhymes, or puns in your subject lines.* Stick with straightforward headlines instead. These “boring” subject lines convert extremely well. That’s because they explain the value inside the email. The readers know exactly what to expect from the message and the benefits they’ll receive from opening it. In fact, here at AWeber, we analyzed our subject line data and found that direct subject lines outperform the more creative ones by an average of 541%. Here are some examples of straightforward email subject lines:

“[Company] Newsletter: July”
“Exclusive workshop invitation from [Brand]”
“Our 10 Most Popular Biceps Workouts”
“The best brownie recipe you'll ever taste."

But there’s one catch: Your messages have to consistently provide value. If your messages fall short of their promised value, your subscribers will feel cheated. Then, good luck getting them to open your messages moving forward. However, if your emails are constantly packed with important, personalized content, your audience will open your emails — no matter what the subject line says. *When your readers trust you and are opening your emails on a regular basis, go ahead and add wit, wordplay, humor, rhymes, or puns to your subject lines! You’ve earned it.

Email subject line rule #3: FOMO

Fear of missing out — FOMO — is a powerful psychological driver of email opens and engagement. Email subject lines that create a sense of urgency, scarcity, and exclusivity can boast a 22% higher open rate, according to the Email Institute. We recently used this technique for our launch of 24/7 Email Marketing Master Class.

Liz from AWeber: "You have one day left to sign up for Master Class!"

And it worked! We saw 5% higher open rates than our regular broadcasts to the same list, and we saw a surge in class enrollments before the deadline, too. We used the FOMO method in a slightly different way for AWeber's Beyond the Podcast Virtual Summit, as well. Here, we touted our active community of podcasters leading up to the event. We asked subscribers to join the group and sign up for the summit.

Beyond the Podcast Summit: "750+ podcasters in the Facebook community. Join them!"

Here are some other examples you can swipe:

Your [offer] ends at midnight
Today only: order your favorites with free shipping
You’re missing out on [offer]
Only 20 spots left at [price]
Urgent: Your subscription is expiring
This weekend only! Get [offer] before it’s gone!

Email subject line rule #4: curiosity

There’s a reason most television season finales end with cliffhangers: Humans crave nice-and-neat endings. So when you don't give it to them, they're unsettled. They have to know what happens next, and they’ll tune in the next season for closure. Use this craving to your advantage. Fuel your subscribers to open your emails by injecting curiosity into your subject lines. You can ask a question:

Jo at Copy Hackers: "Are you missing these 3 copy techniques?"
Men's Health Daily Dose: "Will Creatine Boost Your Gains?"

Or promise an answer inside your message:

Jessica Stansberry: "You should be going live ___ times per month! [open for the answer]"
Sophie Gray: "This is the ONLY Reason You Should Workout"

Or tease a surprise, giveaway, or gift:

AWeber Blog: "We made free summer GIFs for you!"

Or make readers say "huh?!"

Chubbies: "Sincerely, future Dwight"
Really Good Emails: "Emails can be tasty "

Email subject line rule #5: character length

How long should your email subject line be? No one can agree. Litmus recommends around 50 characters. Yes Lifecycle Marketing says emails with subject line up to 20 characters have ethe highest average open rate, unique click rate, and click-to-open rate. An analysis from Retention Science found that subject lines with 6 to 10 words results in the highest open rates. And Return Path advises using 61 to 70 characters. So in reality . . . it depends. (Sorry, I know that’s no one’s favorite answer.) Every industry is different. But here are some important things to keep in mind when you’re testing various subject line lengths — no matter what industry you’re in:

Do most people open your emails on desktop or mobile? If it’s the latter, aim for short email subject lines (35 characters or less).
Is your preview text cut off? If so, will your subject line still make sense without it?
Are there words you can cut to be more concise or clear?
Is your message clear and direct?

Email subject line rule #6: spam triggers

Email spam filters are triggered by specific words, phrases, and symbols in your subject line and email content. AWeber uses a content filtering tool called SpamAssassin™ to help you avoid content filtering. This tool is widely used by ISPs to filter incoming email. AWeber Email Spam Score

By clicking on that score you can instantly view the content in your messages that are triggering the SpamAssassin™ ruleset. So what some words, phrases, and symbols that are red flags to spam filters? Here's a list:

Excessive punctuation like multiple exclamation points!!!!!!! or ellipses ……...
TYPING IN ALL CAPS
Symbols like “$$$” and “*****”
Phrases like “cheap,” “cash off,” “incredible deal,” “satisfaction,” “winner”

For an even longer list of common spam trigger words, check out this list by HubSpot. Also, as many as 69% of email recipients report email as spam based solely on the subject line. Make sure your subject line doesn’t come across as spammy to your subscriber, too. This will happen if your subject line is deceiving in any way, such as leading with “RE:” when it’s not an actual reply to an email.

Email subject line rule #7: emojis

In a busy inbox, an emoji can stand out. In fact, emojis may increase your open rates by 56%, reports Experian.

AWeber Blog: "Why you need a hook 🎣"

While the AWeber content team hasn't seen a rise in open rates whenever we use emojis in our messages, we do continue to use them every so often to pack a punch or to shorten a subject line. (For instance, we might use a 💡 instead of writing out the word lightbulb to keep the entire subject line visible on mobile devices.) On the flip side, some brands — like Product Hunt, a website that curates the best new technology — use emojis in all their subject lines, which makes them recognizable in the inbox over time. When you see an emoji, you know it's probably Product Hunt. Some emojis look very different from one Internet Service Provider (ISP) to the next. So don't forget to test your emails in various ISPs like Gmail, Hotmail, and Yahoo!, too. Here are 3 Ways to Test Your Emails Before Hitting 'Send.' If you choose to use emojis, beware: Emoji usage in marketing messages is on the rise. It's increased at an annual growth rate of more than 775 percent over the last few years, according to mobile marketing automation company Appboy. So your emoji may not stand out as much as you'd like. And almost 1 out of 3 people don't appreciate emojis in email subject lines. Our advice: Test them with your readers. See if your readers act positively to emojis through increased open rates.

Your Takeaways

There's no single formula for writing perfect subject lines. But if you mix-and-match these 7 subject line rules, you'll be able to optimize your open rates over time and come up with a formula that works extremely well with your audience.

Use personalization in your subject lines. Variations of “Hello {!firstname_fix}” are fine, but take it a step further with segmentation. That way, you can send highly targeted emails to an engaged audience.
Be straightforward. It can be tempting to be witty or punny in your subject lines, but until you have the trust of your audience and consistently high open rates, stick with directness instead.
Tap into a subscriber's FOMO. Create a sense of urgency, scarcity, and exclusivity in your subject lines.
Give readers a cliffhanger. Play into their curiosity. Make them want to open to find out the answer!
Test different character lengths. Short, long, somewhere in between — see what works best with your audience (and looks the best on mobile!).
Avoid spam triggers. Keep a list of common words, phrases, and symbols that get stuck in spam filters, and use an ESP like AWeber that gives you a Spam Score for every message.
Be careful with emojis. You can use them to shorten email subject lines or to pack a punch — but make sure your audience actually likes them . Test subject lines with and without them.