How to write subject lines that get your newsletter opened

The subject line is the only thing standing between your newsletter and the archive folder. You can spend hours on the content inside, but if nobody opens the email, none of it matters. So here's what actually works, based on what I've seen across hundreds of newsletters, and what most people get wrong.

What people think works (but doesn't)

There's a whole industry of advice around subject lines that sounds convincing but falls apart in practice. Things like using ALL CAPS for a word, adding "RE:" to fake a reply, or leaning into vague curiosity bait like "You won't believe what happened this week." These might get a click once. They won't build a loyal audience.

The problem with tricks is that they train your readers to distrust you. If someone opens your email expecting something remarkable and finds a standard newsletter, they feel misled. Maybe they don't unsubscribe immediately, but they start ignoring you. And an ignored newsletter is functionally dead even if it's technically still being delivered.

The other common mistake is being too clever. Puns, wordplay, and references that require context to understand are risky. Your subject line is competing with 30 other emails in someone's inbox at 8am on a Tuesday. If it takes even a second of mental effort to parse, it loses. Clarity beats cleverness every single time.

What actually works

The best subject lines share a few characteristics, and none of them are particularly glamorous.

Specificity wins. "5 things that changed in mortgage rates this week" will outperform "This week's market update" almost every time. The first one tells the reader exactly what they're getting. The second one could be anything. When readers know what's inside, they can make a quick decision about whether it's worth their time. And that quick decision is what you want, because the alternative is no decision at all, which means no open.

Useful beats interesting. A subject line that promises the reader will learn something practical or save time will consistently outperform one that just sounds interesting. "How to cut your newsletter production time in half" is useful. "The future of content creation" is vague. People open emails that feel like they'll get something out of them. That sounds obvious, but most subject lines forget this completely.

Short is usually better. Most email clients cut off subject lines somewhere between 40 and 60 characters on mobile. If your key information is at the end of a long subject line, a big chunk of your audience will never see it. Front-load the important words. Get the value proposition in the first five or six words if you can. I've seen subject lines that were genuinely good but performed badly because the most compelling part was hidden behind an ellipsis on mobile.

The curiosity gap (used properly)

Curiosity gaps get a bad reputation because they're so often used lazily. But when done well, they're genuinely effective. The trick is to open a question in the reader's mind that they actually care about the answer to, and to make it clear that the answer is inside the email.

"The one metric most newsletter creators ignore" works because it's specific enough to feel like it matters and open enough to create genuine curiosity. "Something interesting happened" doesn't work because there's no hook, just vagueness.

The distinction is between creating a genuine information gap (where the reader thinks "I want to know that") and being deliberately obscure (where the reader thinks "this is probably clickbait"). One builds anticipation. The other builds distrust.

Length and format considerations

Numbers tend to perform well in subject lines because they signal structure and specificity. "3 tools that improved our workflow" tells the reader this is a list, it's short, and it's practical. Numbers are also easy to scan, which matters when people are flicking through dozens of emails.

Questions can work, but only if they're questions the reader is genuinely asking themselves. "Struggling to grow your newsletter past 500 subscribers?" works if your audience is at that stage. Generic questions like "Ready for your best week yet?" feel hollow because they're not connected to a real problem.

Personalisation tokens (inserting the reader's name) used to move the needle. They don't really anymore. Most people have caught on, and seeing your name in a subject line now feels more like a marketing email than a personal one. I'd skip it unless you have a genuinely good reason.

How to test properly

A/B testing subject lines is one of the most useful things you can do for your newsletter, and most people either don't do it or do it badly.

The basics: split your list into two groups, send the same content with different subject lines, and see which one gets a higher open rate. Most email platforms make this straightforward to set up. We covered the structural elements that make a newsletter perform well in the anatomy of a high-performing email newsletter, and the subject line is one piece of that puzzle.

But here's where people go wrong. They test two subject lines that are too similar ("Weekly Update #47" vs "Your Weekly Update #47") and then draw conclusions from a 0.3% difference. That's not useful. Test meaningfully different approaches. Test a specific subject line against a curiosity-driven one. Test a question against a statement. Test short against long. The bigger the difference between your two options, the more useful the result.

Also, don't over-index on any single test. One A/B test tells you what worked that one time, with that specific content, for that particular audience on that particular day. You need to see patterns across multiple tests before you can draw real conclusions. Run a test with every edition for a month and then look at what themes emerge. That's where the real insights live.

A few things that consistently perform

Based on what I've seen work across different types of newsletters, here are some patterns worth trying.

Subject lines that reference a specific number or data point tend to get above-average open rates. Subject lines that name a specific tool, company, or person tend to outperform generic ones. Subject lines that promise a practical takeaway ("how to" or "a better way to") tend to do well with professional audiences. And subject lines that reference something timely, a recent event, a change in regulations, a new development, tend to get a bump from being relevant right now.

None of these are guaranteed to work for your specific audience, which is why testing matters so much. But they're a solid starting point if you're not sure where to begin.

The honest truth about open rates

Open rates are not the whole picture. They're directionally useful, but they're not perfectly accurate (Apple's Mail Privacy Protection inflates them, for instance) and they don't tell you whether someone actually read or enjoyed your newsletter. A high open rate with low engagement is worse than a moderate open rate with readers who genuinely value what you send.

The subject line gets the door open. The content is what keeps people coming back. Both matter, but if you had to choose where to spend your time, I'd put 80% of your effort into making the content inside genuinely useful and 20% into crafting the subject line. Get the substance right, and the subject line becomes a lot easier to write because you actually have something worth promising.

Cheers