8 email subject line tricks that actually work (with examples)

Your customer sees your email subject line first. And more often than not, it's all they see. If the subject line flops, everything else goes down with it. The body you spent two hours polishing, the visuals, the CTA, nobody will ever see them. No open, no click. And at the end of the chain, no sale.

I work on eCommerce retention every single day, mostly on Klaviyo, and I see subject lines from fashion and lifestyle brands come across my desk constantly. There are patterns that keep showing up in the ones that open well. Here are the ones that come back most often, with an example subject line for each.

But before we talk best practices, we need to sort one thing out. Because if you're basing your decisions on a fake number, you might as well stop right now.

The subject line, and why it makes or breaks everything

The subject line is the first thing your customer reads in their inbox, before they even open. It's also the line that decides whether your email lands in the primary tab or in spam. One single line doing both jobs. So no, it's not a detail.

Everyone wants to know what to write in a subject line. We'll get there, but not with magic formulas. With mechanics I see working on real campaigns.

Your open rate is lying to you (and it's Apple's fault)

Apple Mail Privacy Protection. Since it rolled out, Apple hides the recipient's IP and stops you from knowing who actually opened your email. Except Apple accounts for more than 60% of email opens (Mail, iPhone, iPad). And since many Apple users have the protection turned on, a good share of your measured opens can be inflated, with nobody actually opening.

When you see a 60% open rate on a campaign, that's not 60% of people who read your subject line. A big chunk of it is Apple pre-loading the email in the background. It inflates the number artificially.

That said, open rate isn't dead. It's still useful, but only in relative terms. If you're at 60% on Monday and 40% on Tuesday, you can compare your campaigns against each other and make decisions. Maybe your deliverability dropped, and now you know to go look into it.

But to seriously test your subject lines, you need to go further. On Klaviyo, there's a property called "Apple Privacy Open," true or false for each open. When it's true, the open is attributable to Apple and doesn't necessarily mean much. You build a segment with an "Apple Privacy Open = false" filter. That gives you the real opens.

The segment will be smaller than what you're used to. That's normal. But it's the only one you can test your subject lines on honestly. If you skip this, you'll think a subject line is crushing it when really it's just Apple pre-loading. And you'll end up repeating a mechanic that doesn't work.

Alright. Now that we know what to base things on, here are the 8 tricks.

1. Personalise on behaviour, the first name alone isn't enough

Most brands, when they talk about personalisation, think first name. "Axel, check out our new collection." Klaviyo's data shows that adding just the first name barely moves the open rate at all.

The personalisation that matters is behaviour: the products a customer browses, what they leave in their cart. An email that brings back the pair of boots a customer looked at three times without buying speaks way louder than a first name slapped at the start of a subject line.

For that, all your customer data needs to be centralised in one place. If your data is scattered across your CRM, your email platform and your site, you can't personalise properly. The more clean data points you have on a single profile, the more angles you've got to write a subject line that actually lands.

2. Keep it short, because everyone reads on mobile

The longer a subject line, the fewer people open. It's that simple.

Most opens happen on mobile. And on mobile, a subject line that's too long gets cut off. If the important bit is at the end, nobody sees it. So you write for a phone screen, not a desktop screen.

The average sits around 7 words, emojis included, and those subject lines land around 30% open rate. My advice: test even shorter ones. 4 or 5 words. Put the rest of the info in the preview text.

3. The preview text, the line everyone leaves blank

Everyone obsesses over the subject line and forgets the preview text. It's the little grey text right after the subject line in the inbox. And it's free real estate you're leaving empty for no reason.

Something that works well: lay out the problem in the subject line and slip the start of the solution into the preview. You open a loop in the subject, you drop a hint in the preview. Curiosity does the rest.

Here's an example on a clothing brand. Subject line "Your size is selling out," preview text "We've saved the last pieces in 38 and 40 for you." The subject creates the tension, the preview sharpens it without giving everything away. The person opens to find out.

4. Urgency and scarcity, yes, but not on just anyone

Limited stock, offer ending, private sale closing. Urgency and scarcity make people act. It works. Lines like "last days" or "only a few pieces left" trigger opens.

But watch out. Urgency words, all-caps everywhere, exclamation points on repeat, they no longer wreck your deliverability the way they used to, but they still need to be handled carefully to avoid landing in spam. There's a whole batch of spam-filter trigger words ("free," "100%," "easy money" and the like) that'll dump you into the junk folder if you stack them up. Don't pile them into a single subject line.

And above all, it depends on who you're talking to. A high-intent segment, people who've already ordered from you, will respond well to urgent language. A cold segment, people who barely know you, will find it heavy and mentally flag you as spam. Segment before you push urgency.

5. Build curiosity, but relevant curiosity

Curiosity works hard. A subject line that opens a loop makes people want to open the email to close it. The problem is when the curiosity doesn't match what the customer expects from you, or worse, when the email doesn't deliver on the subject line's promise.

The curiosity gap has to match your audience's intent, and it has to be clearly resolved inside the email. If your subject line says "You won't believe what we found" and inside it's a boring discount on socks, the customer feels played. They'll open once. Not twice.

Bottom line: promise something the customer wants, and keep the promise in the email.

6. Look at what's already filling your customer's inbox

A subject line is never read in isolation. It's read in the middle of 40 other emails. So look at your subscriber's inbox, what do they usually get?

If everyone in your space is throwing emojis and questions into their subject lines, yours is going to blend into the crowd. A bare subject line, no emoji, can stand out precisely because it breaks the pattern. And the reverse is true too. There's no absolute rule, there's inbox context.

That's why blindly copying a competitor's subject lines because they open well rarely works. Their audience and positioning aren't yours, and neither are the rest of their emails. What stands out for them can drown in your inbox.

7. Emojis: one, and only if it fits

Emojis in subject lines, I have a firm take. One, max. And only if it fits your brand and your audience.

On a young lifestyle brand, a well-placed emoji can catch the eye in the inbox. On a brand playing the premium, understated card, an emoji breaks the positioning instantly. It looks cheap. So you test it, and you look at the real open rate, the one filtered from Apple.

8. Test everything, but test clean

All of this is a starting point, not gospel. What works for a leather goods brand doesn't necessarily work for a sneaker brand. The only way to know: test on your audience.

But test clean. Back to the start of the article. If you test two subject lines and look at the raw open rate, you're testing into the void because of Apple. You test on the "Apple Privacy Open = false" segment, you let it run on enough volume so a statistical fluke doesn't fool you, and only then do you decide.

If you test on 200 sends, one subject line at 54% and the other at 48%, be careful. On small numbers, that could just be chance. Wait until you've got volume before drawing conclusions.

Match the subject line to the type of campaign

A marketing email subject line isn't written the same way depending on what you're sending. Same product, same brand, same audience, but the context changes everything.

On an abandoned cart, you can afford to be direct and a little urgent, the person already showed their intent. On a newsletter, it's the opposite: you're sharing info or brand news, you're not selling, so the subject line stays calm. And on a cold segment, go easy, just give a reason to open before pushing anything.

The trap is taking a subject line that crushed it on a private sale and slapping it onto a newsletter. It doesn't work, because the customer's expectation isn't the same at that point in their cycle. Sort your subject lines by scenario: abandoned cart, private sale, newsletter, each with its own. You build yourself a little library to pull from and you don't start from scratch every send.

Where to start

If I had to prioritise: first the real-opens segment, without it everything else is shaky. The fastest win after that is shortening your subject lines and filling in the preview text, that costs nothing. Behavioural personalisation, when you have time, on your abandoned cart flows, product viewed, category browsed. Urgency and emojis, you pull those out for your warm segments and your big moments, private sale launch, new collection, end of sale. Not for everyday use.

A subject line takes 30 seconds to write and it changes everything else. Get them right, test clean, and look at the real numbers.