Subject lines that get opened: how to write your email subject (without clickbait)

The subject is the most important line you’ll write, and also the shortest. It decides, in a couple of seconds, whether your email is opened, ignored or marked as spam. And that last one matters more than it seems: every spam complaint tells Gmail your mail is a nuisance, and that sinks the delivery of all your following sends. The good news: the subject is one of the few things entirely under your control. Let’s see how to write it well.

Short and front-loaded

Most people read email on the phone, where only the first 30 to 40 characters show. If your key message is at the end, no one sees it. Two rules:

Short: aim for about 6 to 9 words, around 40 characters.
The important part first: “40% off, ends today”, not “We’re delighted to announce our seasonal event”. The reader scans; show them the whole message at a glance.

Opens are no longer the metric you think

Here’s a shift almost no one accounts for: since Apple Mail’s privacy protection, many “opens” are fake — the system preloads the tracking image even if no one opened. Your open rate is inflated. That’s why, to know whether a subject really works, look at clicks and the click-to-open rate (CTOR), not opens alone. A subject with lots of opens and few clicks is usually a red flag: it over-promised.

Relevance, not just the name

Dropping in the first name no longer moves the needle on its own. The personalisation that does work is relevance: the subject connecting with what the person did, is interested in or is waiting for. “Your Thursday appointment” or “What you left in your cart” weigh more than a “[Name], we have news”. And use it with judgement — in behaviour-triggered emails, re-engagement or important sends — not in every subject, because overusing it wears it out. How to group for that relevance is in segmentation.

Honesty wins (no clickbait)

This is the point that separates a healthy list from a burned one. A bait subject gets one open; after that it breaks trust, and the unsubscribes and complaints come. The body of the email has to deliver what the subject promises. An honest subject performs better over time than a trick that spikes opens once and then collapses. The trend is clear: people reward clarity over cleverness. If you wouldn’t say it out loud, don’t put it in the subject.

What triggers spam (and what no longer does)

There are surefire ways to land in the spam folder:

ALL CAPS across the whole subject.
Excess punctuation: ”!!!” or ”$$$”. A single ”!” is enough.
Classic trigger words: “FREE”, “100% guaranteed”, “act now”, “make money”.
Fake “RE:” or “FWD:” to fake a conversation.

But beware the word paranoia: the 2026 filters no longer judge by a single word. They score the whole email — content, your sending reputation and how people interact. The word “free”, sent by a sender with a good reputation, doesn’t doom you. Put another way: write naturally; the real levers are your reputation and a well-authenticated domain. That’s why setting up SPF, DKIM and DMARC protects your inbox placement more than avoiding a word.

Formats that work

No tricks, with substance:

Direct benefit: say what’s inside. “Your June statement is ready”.
A number or specific fact: “3 ways to fill your slow Tuesdays”. The concrete beats the vague.
Curiosity anchored in value: “The metric almost everyone ignores” opens a loop, but a relevant one. None of that “you won’t believe this”.
A specific question: “Do you confirm your Thursday appointment?”. It calls the reader in and is clear.
Real urgency: “Ends today” works if it really ends today. Invented urgency shows.

The preheader is your second subject

That grey text next to the subject — the preheader — is, in practice, a second subject line. Don’t waste it leaving it as “View this email in your browser”: write it on purpose, in pairing with the subject, to complete the message. Used well, it lifts opens noticeably.

Test, don’t guess

The best subject isn’t intuited; it’s tested. How to run an A/B test that’s worth it:

One variable at a time: length, or personalisation, or question vs statement. If you change everything, you won’t know what moved the needle.
Split it: send version A to 20% of the list, B to another 20%, and the winner to the remaining 60%.
With a big enough sample and no rushing: don’t declare a winner in ten minutes.
Measure clicks, not just opens. And remember: your own past sends teach you more than any list of rules.

In Panama: how we solve it

Writing short, honest, relevant subjects, pairing them with the preheader, testing them against your data and keeping your reputation clean is part of what we do in segmented email marketing. We don’t guess: we test and measure by clicks, not by inflated opens, so your emails arrive and get opened without mistreating your list.

Do your emails get opened as much as they should? Start with the free check: we review your subjects and your deliverability, and tell you what to adjust first.