Email Marketing Subject Lines – How to Write Ones That Get Opened & Convert

Your email is only as good as its subject line—if no one opens it, nothing else matters. You could have the best content, an irresistible offer, or a game-changing product inside, but if your subject line is weak, your email is dead on arrival.

Most emails get ignored because their subject lines are boring, vague, spammy, or worse—get flagged by spam/promotion filters. If you’ve ever wondered why your emails aren’t getting the engagement they deserve, chances are your subject lines are the problem.

But don’t worry. This guide will show you how to craft compelling email marketing subject lines that get opened, read, and acted upon.

Why Subject Lines Matter

  • First Impression Counts – The subject line is the first thing people see in their inbox, and it determines whether they open or delete your email.
  • Direct Impact on Open Rates – A strong subject line can make or break your campaign, affecting your email’s success.
  • Inbox Competition – Your email is fighting for attention against dozens (if not hundreds) of others every single day.
  • Spam & Promotions Filters – Poorly crafted subject lines can land your email in the spam or "Promotions" tab, significantly reducing its reach and impact.

The Psychology of High-Performing Subject Lines

What makes a subject line irresistible? It’s all about psychology.

  • Curiosity & Intrigue – Subject lines that leave readers hanging encourage them to open the email. (e.g., "This one mistake could be killing your sales...")
  • Urgency & FOMO – Deadlines and limited-time offers create a fear of missing out. ("Only 3 hours left to grab 50% off!" or "Only 5 left in stock!")
  • Personalization – Emails with the recipient’s name or a relevant topic see higher open rates. ("John, your exclusive deal is inside!")
  • Clarity & Relevance – If your subject line is too vague or misleading, people won’t trust it. ("How to double your conversions in 7 days")

Proven Subject Line Formulas That Work

Want an easy way to write compelling subject lines? Use these proven formulas:

  • The Curiosity Hook: "You’ll Never Believe What We Just Launched..."
  • The Urgency Play: "Final Hours: 50% Off Ends Tonight!"
  • The Personal Touch: "John, Here’s Something Just for You!"
  • The List Format: "5 Email Hacks to Boost Your Open Rates"
  • The Question Approach: "Are You Making This Email Mistake?"
  • The How-To: "How to Instantly Improve Your Email Open Rates"

What to Avoid in Email Subject Lines

Just as important as what you should do is what you shouldn’t do:

  • Spam Triggers – Words like "free," "act now," and excessive exclamation points can land you in spam.
  • Clickbait & Deception – If your subject line misleads, people will lose trust in your emails.
  • Too Long or Too Short – Ideal subject lines are 6-10 words or 30-50 characters for best results.
  • ALL CAPS & Overuse of Emojis – These make your email look unprofessional or spammy.
  • Words That Trigger Promotions/Spam Filters – Avoid "huge sale," "winner," "congratulations," and other flagged phrases that send you straight to the Promotions tab.
  • Reused Subject Lines – Using the same subject line repeatedly can cause emails to stack into a thread, making your message get buried and ignored.

Understanding Email Deliverability

Email deliverability determines whether your emails land in the inbox, spam folder, or never get delivered at all.

Several factors influence this:

  • Blacklists – If your domain or IP address is flagged for spam, your emails could be blocked entirely. This isn't abnormal for some blacklists-the more your domain appears on the higher likelihood your email will hit junk/spam. You can see if your domain is on blacklists using this Free tool
  • Email Content – Spam filters scan subject lines and email content for trigger words, excessive links, and poor formatting.
  • Email Size – Large emails with excessive images or attachments can increase the likelihood of getting filtered.
  • Opt-In Method – Emails sent to people who didn't explicitly subscribe increase complaints and hurt your sender reputation. Ensure your subscribers actually signed up to your list for better deliverability.

A/B Testing & Optimization

Even the best subject line strategies require testing. Here’s how to optimize:

  • Why Testing Matters – Find out what works for your audience by running different subject lines.
  • How to A/B Test – Send two versions of the same email with different subject lines and compare the open rates. Only ever test 1 variable at a time for consistent results.
  • Tracking Metrics – Measure open rates, click-through rates, and conversions to see which subject lines perform best.

Next Steps

Mastering email marketing subject lines is the key to boosting open rates, engagement, and conversions. Without a strong subject line, your email won’t stand a chance.

What’s Next?

Start applying these strategies to your next email campaign and test different subject line formulas to see what resonates with your audience.

Need expert help? Get help crafting an entire email system for your business, click here to see my service.

Want to learn how to use AI to craft high-converting subject lines and email copy? Grab my Free AI Copywriting Playbook today.