If I had a quid (£1 for those of you not from the U.K) for every time I’d received email marketing copy without a subject or a pre-header, I’d be a rich man, maybe not enough to retire on, but you get the idea.

Despite Email Open Rates being considered a vanity metric by many in the email marketing industry, writing compelling subject lines still plays a crucial role in the overall success of every email campaign you send, and it’s often overlooked.

I can’t count how many times I’ve sent copy back and asked what the subject line is. Often met with ‘Oh, let me come up with something quickly’ or ‘Just use this, it will do’

Next to your Sender Name, your subject line is the first thing people see when they scan their inboxes and try to decide, out of the hundreds of emails they get weekly, whether yours is going to get opened or not.

Think about your own inbox, have a quick scan now, how many really jump out and grab your attention?

As email marketers, we have to work hard, really hard, to get our emails noticed, so it’s super, super important that we spend some time thinking about what we write. What is going to grab our readers’ attention, while still delivering on what the content of the email contains.

To master writing compelling email subject lines, you must first understand that you are designing for the small screen. With over half of all emails now opened on mobile devices, brevity is your best friend. Aim to keep your subject lines under 50 characters to prevent them from being cut off mid-sentence.

Beyond length, a successful subject line should be:

• Personalised: Including the recipient’s first name can increase the chance of an open by nearly 15%.
• Relevant: Use data like location or past purchase history to make the email feel hand-crafted rather than part of a mass broadcast.
• Urgent or Curious: Spark interest with a question or a time-limited offer to encourage immediate action

If you are struggling to start, these proven formulas can provide a solid foundation:

• The Data Formula: Highlighting a specific, unexpected statistic (e.g., “Why 19% of graduates can’t find work”) piques interest and curiosity.
• The Inquiry Formula: Asking a direct question often outperforms a standard statement (e.g., “Have you heard about our sale?” vs. “Sale now on”).
• The Personal Touch: Combine a name with a relatable situation, such as “John, are you a zombie without your morning coffee?”

Writing a great subject line is as much about what you don’t do as what you do. To maintain your sender reputation and avoid the dreaded junk folder, steer clear of the following:

• Aggressive Punctuation and Casing: Avoid shouting at your readers. Using all caps or multiple exclamation marks (e.g., “OPEN NOW!!!!”) is a major red flag for spam filters.
• Spam-Trigger Words: While “free” can sometimes be effective, overusing aggressive sales language like “BUY NOW” or “CASH” can trigger filtering.

Deceptive Clickbait: Never mislead your audience. If your subject line promises a 50% discount but the email content doesn’t deliver, you will destroy subscriber trust and see a spike in unsubscribes. This is arguably the biggest mistake to avoid. DON’T do it.

Finally, remember that no one is perfect. If you do make a mistake—such as sending a broken link or a premature promotion—a well-handled “Oops” or “Correction” subject line can actually see some of the highest open rates as it shows a human side to your brand, but whatever you do, don’t fake this, your subscribers will suss you out and you’ll lose credibility quicker than a premier league manager who refuses to adapt his system to the players he has.

The only true way to know what resonates with your specific audience is through A/B testing. Try sending two different subject line styles to a small segment of your list and use the winning version for the rest of your send. This data-driven approach removes the guesswork and ensures you are constantly improving your results.