Part 2: How to Write Compelling Subject Lines

Ultimately, your email campaigns’ open rate comes down to the appeal of your subject line. All the email marketing tricks in the book won’t entice people to open your email if the message isn’t compelling.

This is where copywriting comes in. It’s not easy to capture people’s attention and convince them to click in mere milliseconds — but that’s what you need to do with your email subject line.

In the first part of this blog, we explained how to use the CURVE method to craft a great subject line. Now, let’s dig down into the mechanics of it: how to choose the right words, tone, and rhythm to make your subject line appealing.

Why good copywriting is crucial to email marketing success

Contrary to some opinions that email marketing is old-fashioned, it is on the rise, with 89 percent of marketers using it as their primary source of leads. Meanwhile, a staggering 306.4 billion emails were sent in 2020, and that number will likely increase.

With all these emails coming in, users are making snap judgments in their inboxes. What’s the main influence on their decision? That’s right, the subject line: 47 percent of users decide whether or not to open an email based solely on this.

“Subject line” is a bit of a misnomer: the phrase stems from the use of email for one-to-one communication, in which it’s standard practice to tell your friend or coworker what your email is about. But just as subject lines such as “Read this!” are annoyingly vague, generic subject lines of marketing emails are not compelling. Nowadays, they seem spammy.

Rather than simply describing the topic of your email, a good subject line speaks to your recipient’s curiosity and emotion. It must persuade them to take time out of their day to open and read your email. At the heart of persuasion is copywriting.

Copywriting best practices to use in your email marketing

Copywriting is all about using the right words to inspire action. Despite what some people will tell you, no one formula delivers results. That’s because your target audience is unique, as is your relationship with them. You need to speak to them in a way that resonates — and that looks different for different brands.

That said, there are some best practices of copywriting that can make your subject lines much more compelling. Once you have a firm grasp of your audience and what they want to hear, put these best practices into action.

Keep it short and sweet.

People have short attention spans, so you need to be able to instantly grab their attention. Keep your email subject lines short. This will also ensure that they aren’t truncated by your recipients’ email programs.

The #1 mistake people make in persuasion is being verbose. They assume that more words equals more convincing. This isn’t true. In fact, you can quickly lose your audience’s attention. Don’t stuff your subject lines with a bunch of words.

Take this subject line for example:

“[Name], identify the right tools and skills to optimize your marketing performance”

This sentence is 12 words long, and at least three of those words could be swapped out for simpler synonyms. It’s also not saying anything exciting: it reads a bit like a course syllabus!

Avoid adding more words to sound more authoritative or compelling in your email marketing. Often, this has the opposite effect — it makes your email sound pretentious and boring.

Make it actionable, not sales-y.

Yes, copywriting is part of selling. But the best copywriting is not “Open now for amazing deals!” or “You won’t believe this special offer.” Those phrases are simply fluff, not anything that entices someone. Your goal is to make them take time out of their busy day, so your subject line should express a benefit that they can take action on.

Also, your recipients know that you want them to open your email. Overtly asking them to do so may work for some brands, but be cautious about stating the obvious. Remember the CURVE method: Curiosity is first on the list!

Use active language.

Copywriting is all about persuasion, so if you distance yourself (or your recipient) from the topic, you’re sending a powerful subconscious message: there’s nothing urgent about this email. This is what passive sentences do.

A passive sentence either (a) places the action of a sentence first or (b) strips the subject (the doer) from the sentence. It often has a version of the “to be” verb, such as “have” or “has.”

Here is an example of a subject line written in passive language:

“New fall styles have arrived in our store”

There is no human actor anywhere in this sentence. It sounds like the products just happened to show up in the store’s inventory. This subject line doesn’t connect with the recipient’s desires; it doesn’t even imply an action for them to take.

If the recipient ostensibly wants to indulge in new fall fashions, a better subject line would read:

“Be the first to explore new fall styles”

This subject line is active. It is written in an imperative mood, meaning that it instructs the recipient to do something. The verb is exciting, and the object of the action (“new fall styles”) is saved until the end. This subject line has both curiosity and urgency, plus a spot of FOMO that taps into emotion.

Case Studies: Do’s and Don’t’s of Subject Line Copywriting

Consider these real-world examples:

  1. [Name], there’s only a few hours left to enroll in my course
  2. Discover new digital marketing skills to improve your skills and grow your business
  3. Exciting update! [Name], your next car is at your fingertips with our auto financing

Not only are these subject lines very long, to the point of being cut off in the inbox view, but they’re also boring. Example #1 has urgency, which is good, and is personalized to the recipient. However, it creates distance between the user and the action. “There’s only a few hours left to enroll…” does not urge the recipient to do anything. A better example may be:

“[Name], you have just 5 hours to enroll in my course!”

However, this subject line still lacks Curiosity, Relevance, Value, and Emotion. We’d recommend the copywriter go back to the drawing board and figure out the benefit being offered to the recipient.

Example #2 keeps the focus on the recipient and expresses a benefit — but it takes a whopping 83 characters to do so. Also, the word “skills” is used twice. This subject line is just too wordy, and it lacks urgency and emotion. A better example would place the benefit first:

“Grow your business with these new digital marketing skills”

Here, the user reads the benefit (“grow your business”) first, then gets a teaser of how to do it. And this subject line is only 58 characters — ideal for most inboxes.

Example #3 is also way too long, starting with the unnecessary “Exciting update!” and concluding with the redundant “with our auto financing.” A much simpler version would perform better:

“[Name], your next car is at your fingertips.”

Short, sweet, and intriguing.

Three quick tips for the perfect subject line

Here’s your convenient cheatsheet for crafting compelling subject lines:

1. Put the most important message first

In journalism, there is a concept calling “burying the lede,” i.e. when writers don’t explain the core story until one or more paragraphs in. Above, we shared examples of subject lines that “bury the lede” by putting the core message at the end of the sentence.

Assume that your audience will only skim the first few words of each subject line. Will yours grab their attention, based on that?

Also, remember that your recipient is more important than your offer. By prioritizing their interest, you can make your subject line resonate with them. Write active sentences to keep the focus on them.

2. Never mislead or trick your audience

Ever seen a subject line that began “RE:” but was actually a marketing email? Or one that attempted reverse psychology, e.g. “Don’t open this email”? These tactics may seem clever, but many recipients will regard them as dishonest and manipulative.

Think of it this way: your recipients are sifting through hundreds of emails and making snap decisions about which ones to open. You must speak to their desires and emotions if you want to cut through the noise. Making them feel bad about themselves will quickly backfire.

Avoid the following language in your subject lines:
“Act now”


“Must read”

Here are more bad examples of manipulative subject lines:

“If you want to miss out, just ignore this email”

“You’ll regret not opening this email”

“RE: re: your new business”

If you want to tease an offer, keep the focus on your company. Evaluate whether your brand’s voice meshes with a snarky or tongue-in-cheek tone. For example:

“We’ll be sad if you miss this deal!”

“We’re really excited to share this with you…”

Use these sparingly, though: you still want to use the CURVE method in most of your subject lines.

3. Be authentic and honest

It can be a fine line between teasing a benefit and making wild promises. Avoid being “clickbait-y” with subject lines such as “You won’t believe these deals!” Your email recipients can sniff out insincerity, and they don’t like overt grabs for attention. They may even consider your email to be spam.

Bad examples:

  • “Open now for major savings”
  • “We know you’ll love this”

Good real-world examples:

  • “Bring home the fun + take an extra 15% off”
  • “Ahem. New handpicked (well, robot-picked) recommendations are ready

See the difference? The subject lines in the first set are sales-focused and generic. The second one may even be considered presumptuous. Both are technically active-language and short-and-sweet, but they’re also demanding and vague.

By contrast, the subject lines in the second set are intriguing. The first one leads with the benefit and simply tacks on the savings reference. The second one is technically a passive sentence, but we’ll let it slide for its sense of humor and attention-grabbing copy. (How many subject lines do you see that start with “Ahem”?) Both come off as more authentic and personable, rather than screaming “buy, buy, buy!”

How to write great copy without triggering spam filters

Unfortunately, even a well-crafted subject line can accidentally land your email in the spam box. That’s because certain words are common red flags of unsolicited email. Most email providers immediately dump emails with spammy words — even if the recipient subscribed to the emails!

One solution is to ask your recipients to whitelist your email when they sign up. However, it’s a best practice to avoid any words or phrases that trigger the spam filters.

As of 2021, there are more than 500 trigger words and phrases — and many of them are frequently used in sales emails. That’s precisely why they’re considered red flags.

Common Trigger Words:






Common Trigger Phrases:

“Be your own boss”

“Act immediately“

“See for yourself”

“What are you waiting for?”

You can view the whole list here.

This isn’t to say you can absolutely never use any of these words. If you have a good sender reputation, email programs are less likely to mark your email marketing efforts as spam. The occasional inclusion of “free” or “limited-time” won’t destroy your email campaign, but we recommend flexing those copywriting muscles to create a unique alternative unless absolutely necessary.

However, if you use the CURVE method and the copywriting best practices we described above, you’ll find less need to use those trigger words and phrases. Notice that most of them refer to the special offer or money in some way. As we discussed, you want to keep the focus on the benefit for your audience. You should also avoid demanding or generic phrases.

Work on creating unique, clever subject lines, and you’ll be able to drive up your open rate and stay out of the spam box.

Wrapping up

You’ve now learned the CURVE method and the copywriting techniques that will help you craft compelling subject lines and improve your email marketing ROI. In part three of this series, we’ll look into why personalization of the From and To fields, as well as body copy, is crucial to your campaign’s success.

Bert-Jan van Rein
Owner Qamel/B2B marketing automation and email marketing strategist and consultant
Helping B2B and charity organizations to improve revenues with marketing automation and email. Supple integration with all online marketing activities is paramount. Together with my fellow workers at Qamel we provide services and tools for lead nurturing.