How to write a subject line for an email is one of the most important skills in modern marketing, because your subject line decides whether your message gets opened or ignored. When you know how to make it the right way, using clear value, curiosity, and simple psychology, you instantly boost your open rates and get more people to read what you send.
So, what actually makes a subject line work? – Clarity, curiosity, and relevance.
But the long answer is far more interesting and far more powerful once you understand it.
Why Most Subject Lines Fail
Tons of emails never get opened, not because they’re bad emails, but because they’re invisible. Here are the common reasons subject lines flop:
1. They’re too vague
When I say “They’re too vague,” I mean the subject line doesn’t tell the reader anything useful, interesting, or specific. “Checking in,” “Quick question,” and “Following up” give zero incentive to open. People see dozens of these daily. These phrases don’t explain what the email is about, why it matters, or what benefit the reader gets by opening it.
Instead of saying “Checking in,” etc try something like: “Checking in about your order status”, or “Found something on your website worth fixing”, ”A collaboration update that could benefit us both”.
2. They try too hard to be clever
Creativity is great. Confusion is not. Because when someone sees a subject line, their brain asks one question: “What is this about, and do I care?” If someone has to guess what the email is about, they’ll skip it. People don’t have time to decode a clever joke or puzzle.
Instead of: “We finally did the thing!” Try: “New feature we just launched – here’s what it does”
3. They lack a clear benefit
People don’t open emails for fun; they are busy. They scroll through emails fast. They open them to save time, solve a problem, learn and improve something or get a deal. A subject line with no clear benefit doesn’t tell the reader what they will get or why opening the email is worth their time.
Try: “Quick idea to improve your website conversions”, “3 tips to fix slow email open rates”, “Download your free checklist”. No, “Just checking in”, “Update”, “Quick question”.
4. They look automated
When a subject line looks automated, it feels like it was sent by a robot or a mass email system, not a real human. These lines don’t feel personal or relevant: “ACCOUNT NOTICE #2049”, “LAST CHANCE TO SAVE MONEY!!!”, “PROMO: LIMITED TIME ONLY!!!”
People are more likely to open emails that feel personal and human, like someone wrote them specifically for them. Try with “Quick update about your account”, “A small question about your project”, “Here’s something helpful for you”.
5. They feel clickbait-y
“YOU WON’T BELIEVE THIS!” or “READ NOW!!!” might get attention and hype, but not trust. It doesn’t feel honest or professional. And without trust, open rates and future deliverability drop.
6. They ignore user intent
If your subject line doesn’t align with what the subscriber actually wants to receive, it won’t work.
You can also check out my detailed guide for deeper email marketing insights.
7 Proven Subject Line Formulas
These formulas consistently perform well across industries because they tap into clear, simple human psychology.
1. The “Benefit First” Formula
This formula works because it instantly shows the reader what they will gain from opening your email. People care about results, solutions, and improvements
Examples:
- “How to cut your writing time in half this week”
- “A simple tweak that boosts your conversions instantly”
This works because it answers the reader’s most important question: What do I get from opening this?
2. The Curiosity Gap
The curiosity gap is when your subject line gives just enough information to spark interest… but not enough to satisfy it. Always give your subscribers information in small portions. This creates a natural curiosity gap that encourages them to open the email to learn more.
Examples:
- “This one habit changed everything for me…”
- “I wasn’t expecting this—”
Tip: Curiosity works best when paired with relevance. Make sure the email actually delivers on what the subject suggests.
3. The “Short and Direct” Line
Short subject lines work because they stand out in a crowded inbox. When everything else looks long and promotional, a simple two or three-word line feels personal.
Examples:
- “Quick idea”
- “Small request”
- “Let’s fix this”
These feel like messages from a real person, not a marketing department.
4. The “How-To” Subject Line
“How-to” works incredibly well because it instantly promises practical value. The reader knows they’re about to learn something useful, and the benefit is clear right from the start. This style is especially effective for educational content, tutorials, tips, and problem-solving emails.
Examples:
- “How to double your client referrals”
- “How to storyboard your next video in 10 minutes”
People love simple, straightforward solutions.
5. The List Formula
Numbers in your subject line to show the reader exactly what they’re going to get.
Examples:
- “7 mistakes killing your open rates”
- “5 shortcuts every freelancer should use”
Odd numbers tend to outperform even ones, but both work.
6. The FOMO Subject Line
Humans naturally want to avoid losing opportunities, deals, or important information. When used lightly, FOMO (Fear of Missing Out) can lift open rates massively and it’s one of the most powerful psychological triggers you can use in a subject line.
Examples:
- “Last chance to register”
- “You’re missing something important…”
- “Only a few spots left – don’t miss this”
But just don’t overuse it; Use it carefully. If you create fake urgency or use FOMO too often, readers will stop believing you, and that can damage trust, unsubscribe rates, and even future email performance.
7. The Personalized Call-Out
Not the spammy “[FIRST NAME], OPEN THIS!” type, but subtle. That kind of personalization feels spammy and fake. Real personalization is subtle, relevant, and focused on the reader’s specific interests or situation.
Examples:
- “A quick tip for your YouTube growth”
- “Something that might help your store this month”
This works because it feels tailored, not automated.
Power Words and Psychological Triggers
Certain words instantly draw attention, evoke emotion, or trigger action. Sprinkle them lightly, don’t stuff them.
1. Urgency Words
- today
- now
- limited
- expires
But always ensure the urgency is real.
2. Curiosity Words
- surprising
- unusual
- hidden
- secret
These create intrigue without sounding clickbait-y.
3. Value Words
- proven
- step-by-step
- simple
- practical
They communicate real usefulness.
4. Emotional Triggers
Emotion, even subtle emotion, drives action.
- finally
- struggle
- effortless
- frustrating
People open emails that speak to their real experiences.
5. Authority Words
- expert
- research-backed
- data-driven
These add credibility, especially in educational or analytical content.
Personalization Rules (What Works vs. Spammy Tactics)
Personalization is powerful, but only when it feels natural. Misused, it comes off creepy or automated.
What Works:
1. Contextual personalization
Referencing something relevant to the reader’s interests or behavior:
- “A better way to manage your Shopify orders”
- “Saw you downloaded our template, here’s what to do next”
2. Using names sparingly
You can use their name occasionally, but never overdo it.
Example that works:
- “Maria, a quick idea for your homepage”
3. Segment-based relevance
Sending different subject lines to different audiences, beginners vs. advanced users, leads vs. customers, active vs. inactive subscribers.
What Feels Spammy:
- Shouting their name (“MIKE! READ THIS NOW!”)
- Fake personal intimacy (“Hey bestie, guess what?”)
- Pretending the email is a reply (“RE: our chat”) when no chat happened
- Using misleading personalization tokens that break (“Hi {FNAME}”)
People love personalization only when it’s authentic and helpful.
How to Write a Subject Line for an Email
Below are subject lines that have universally high open rates across industries. You can adapt them directly:
1. For marketers and creators
- “Your content plan for next week (copy this)”
- “A quick win you can use today”
2. For e-commerce
- “Your wishlist item is on sale”
- “Before you check out, something you’ll want to see”
3. For coaches and consultants
- “This might help you book more clients”
- “A mistake I used to make (and how to fix it)”
4. For newsletters
- “5 ideas worth stealing this morning”
- “A smarter way to start your week”
5. For cold outreach
- “Idea for your website”
- “Question about your growth plan”
6. For re-engagement
- “Still want to hear from us?”
- “We kept this just for you…”
Use them as inspiration, but always tweak them for your brand voice and audience.
A/B Testing Basics
Even the best advice is still a guess until your audience confirms it. A/B testing makes sure your subject lines are chosen based on data, not intuition.
Here’s how to test properly:
1. Test only one variable at a time
If you change too much, you won’t know what made the difference.
Try things like:
- tone (formal vs. casual)
- length (short vs. long)
- format (question vs. statement)
- personalization vs. no personalization
2. Use a meaningful sample size
Testing on only 50 people (or any very small group) won’t show reliable data, the results can be random or misleading. A good rule of thumb is to test your subject line on 20-30% of your email list each time. This gives you a large enough audience to see true differences in performance
3. Test over enough time
Open rates can change throughout the day as people check their inbox at different times. If you look at the numbers after only 30 minutes, you’ll get an incomplete picture.
To get accurate results, let the test run for at least 24 hours. And if your audience is spread across different time zones, it’s even better to wait 48 hours. This ensures everyone has a fair chance to see the email, giving you more reliable data to compare which subject line truly performed better.
4. Learn from patterns
A/B testing becomes truly powerful when you look for patterns in what your audience responds to. Over time, you’ll notice certain styles winning again and again.
- straightforward benefit-driven subject lines,
- subject lines that use a touch of curiosity, or
- short, simple messages that feel personal.
Once you see patterns, you can create a reliable subject line style specifically tailored to your readers.
What NOT to Do (Spam Triggers)
Even with a good subject line, certain words and tactics can push your email straight to the spam or promotions tab.
Avoid:
1. Excessive punctuation
- “Open this NOW!!!!”
- “$50 OFF TODAY ONLY!!!”
Too many exclamation marks or overly dramatic punctuation can make your subject line look spammy and unprofessional.
2. All caps
Writing your entire subject line in all caps makes it look aggressive, unprofessional, and overly promotional. It’s a common spam signal, and both readers and email filters treat it as a red flag. Using normal capitalization feels more genuine and trustworthy.
Avoid:
“IMPORTANT UPDATE ABOUT YOUR ACCOUNT”
3. Overusing sales language
Words like “FREE!!!”, “Act now!”, “Guaranteed!”, “WINNER!” can trigger filters and is often associated with low-quality promotion.
4. Misleading subject lines
If you promise one thing and deliver something completely different, readers feel tricked. That frustration often leads to unsubscribes, spam reports, and a drop in trust.
5. Over-personalization
Aggressive personalization feels creepy, especially in cold outreach. When you use a subscriber’s name too often or reference details that feel too personal or unnecessary, it can come across as intrusive instead of helpful.
Avoid:
“John, I saw you were online at 3:17 PM yesterday…”
6. Repetitive phrases
If your subject lines always repeat the same urgency tactic, filters catch on. Repetition reduces impact. When the urgency is always the same, people stop believing it.
7. Clickbait tactics
When you use dramatic or exaggerated promises just to get a click, readers feel misled. It’s the classic case of short-term gain, long-term destruction.
8. Too many emojis
One emoji can work. Five looks like spam.
Conclusion
Great subject lines aren’t magic, they’re psychology, clarity. Writing subject lines that get higher open rates doesn’t have to be complicated. The key is to stay clear, honest, and focused on what your reader actually cares about.
When you highlight real benefits, create natural curiosity, personalize your message, and avoid spammy tactics, your emails instantly become more appealing. Test different styles, watch what your audience responds to, and use those patterns to guide your future subject lines. With a little practice and consistency, open rates stop being unpredictable, and you’ll start creating subject lines that people want to open, and your email results will keep getting better.
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