Open your email client right now and look at your inbox. For every email, you'll see three things: the sender name, the subject line, and a short snippet of text that follows it. That snippet — the preheader, or preview text — is one of the most underused pieces of real estate in email marketing.
Most businesses either leave it blank entirely, repeat the subject line word for word, or end up with whatever their email platform decides to pull from the body copy. In most cases, that means your subscribers see something like "View this email in your browser" or "Having trouble viewing this email?" — directly beneath your carefully crafted subject line.
That's not just a missed opportunity. It's actively undermining the open you're trying to earn.
This guide covers what a preheader actually is, why it matters more than most people realise, exactly how long it should be on every major client, and how to write one that works as a genuine teaser — the second sentence of a two-sentence pitch that earns the open.
What is email preheader text?
Email preheader text — also called preview text — is the short snippet of copy that appears directly after the subject line in most email clients' inbox views. It's typically 40–90 characters long depending on the client and device, and it's visible before the email is opened.
Here's what it looks like in a real inbox:
Now imagine the same inbox without a preheader set:
The difference is stark. The first version uses the preheader as a genuine extension of the subject line — it adds new information, creates curiosity, and gives the reader a reason to open. The second version wastes that space entirely, handing the choice over to whatever text happens to appear first in the email HTML.
How long should your preheader be?
This is where it gets nuanced — and where most guides fall short by giving you a single number. The reality is that different email clients show different amounts of preheader text, and the amount shown also depends on how long your subject line is.
Here's what each major client actually shows:
| Client | Subject limit | Preheader shown | Combined visible |
|---|---|---|---|
| iPhone Mail (Pro Max) | ~47 chars | ~90 chars | ~130 chars total |
| iPhone Mail (standard) | ~41 chars | ~75 chars | ~110 chars total |
| Gmail app (mobile) | ~38 chars | ~60 chars | ~90 chars total |
| Outlook app (mobile) | ~50 chars | ~70 chars | ~110 chars total |
| Gmail (desktop) | ~70 chars | ~100 chars | ~160 chars total |
| Outlook (desktop) | ~60 chars | ~80 chars | ~130 chars total |
The key insight from that table: the preheader and subject line share a fixed visible space. A longer subject line leaves less room for the preheader. A short subject gives the preheader more room to breathe.
The practical target: 50–90 characters for the preheader, with the most important words in the first 50. That ensures your core preheader message is visible even on the most restrictive client (Gmail mobile, ~60 chars of preheader space).
How to write a preheader that earns the open
Think of the subject line and preheader as a two-sentence pitch. The subject line is the headline — it captures attention. The preheader is the hook — it converts that attention into an open.
The best preheaders do one or more of the following:
1. Extend the subject — add new information
The most common preheader mistake is repeating what the subject line already said. If your subject says "Your March update is here", a preheader that says "March update inside" adds nothing. The reader already knows there's a March update — that's literally what the subject said.
2. Write it as a teaser — create just enough curiosity
The preheader doesn't need to summarise the email. It needs to make the reader want to find out what's inside. A slight information gap — a hint at something specific without fully revealing it — is far more compelling than a complete description of the email's contents.
3. Include a soft call to action
Preheaders that include action language — "see what's inside", "find out more", "here's what to expect" — consistently outperform passive descriptions. The action language creates forward momentum and frames the open as a small, easy step rather than a commitment.
4. Use numbers for specificity
Numbers create credibility and set clear expectations. "Five things worth reading this week" is more compelling than "Some things worth reading this week" because the number signals that the email is structured, curated, and worth the reader's time.
5. Ask a question
A well-placed question in the preheader triggers the brain's curiosity response — the same reason question-based subject lines perform well. The reader needs to open the email to resolve the tension the question creates.
The four preheader mistakes to avoid
1. Leaving it blank
Already covered — but worth reiterating. A blank preheader means the email client picks the text for you. It will always pick wrong. Set one. Every time. Without exception.
2. Starting with a browser link
Many email templates include a "View this email in your browser" link at the very top of the HTML. If you don't set a dedicated preheader field in your ESP, this is exactly what subscribers will see in their inbox. Check your ESP's preheader settings — most have a dedicated field that injects hidden text before the browser link.
3. Repeating the subject word for word
Some ESPs auto-populate the preheader from the subject line. If yours does this, override it manually every time. Identical subject and preheader is worse than no preheader — it signals laziness and wastes the available inbox space.
4. Writing it too short
A preheader of 10–20 characters is barely visible on any client. You're filling in the field without actually using it. Aim for 50–90 characters — that's enough to say something meaningful without being cut off on the strictest mobile client.
The Preheader Optimiser — what it checks
I built the LiamMail Preheader Optimiser to solve the "I set one but I don't know if it's any good" problem. You enter your subject line and preheader, and it shows you exactly how they look together across every major client — and scores your preheader against seven criteria.
Preheader and subject line — using them as a pair
The most effective inbox previews treat the subject line and preheader as a single unit — two halves of the same pitch, written together rather than the preheader being added as an afterthought.
A useful exercise: write your subject line first, then ask yourself what the most compelling thing is that you could say next — the one thing that would make someone who almost scrolled past stop and open. That's your preheader.
If you're struggling to write the preheader, it's often a signal that the subject line itself is too vague. A specific, well-written subject line almost suggests its own preheader. A generic one doesn't — because there's nothing specific enough to extend.
The Subject Line Tester and Preheader Optimiser are designed to be used together for exactly this reason. Test your subject line first, refine it, then check the pair as a unit in the Preheader Optimiser to see how they render side by side across every major client.
Quick reference — preheader dos and don'ts
- ✅ Always set a dedicated preheader — never leave it blank
- ✅ Aim for 50–90 characters — front-load the key message in the first 50
- ✅ Extend the subject line — add new information, not a summary
- ✅ Write it as a teaser — hint at what's inside without fully revealing it
- ✅ Include a soft CTA — "see what's inside", "here's what to expect"
- ✅ Use numbers and questions for specificity and curiosity
- ✅ Check the subject + preheader pair before every send
- ❌ Don't repeat the subject line — even partially
- ❌ Don't let the browser link become your preheader
- ❌ Don't write fewer than 30 characters — you're wasting the space
- ❌ Don't summarise the whole email — tease, don't tell