An email preheader is the short preview text displayed next to or below the subject line in most email clients. It acts as a secondary subject line — a second bite at convincing someone to open. When left unset, clients pull random body text instead, which almost always hurts open rates.
Most marketers spend 80% of their email effort on the body and forget the two lines that decide whether anyone reads it — the subject line and the preheader. Getting both right is the lowest-effort, highest-return move in an email programme.
What is an email preheader?
The preheader (also called preview text or the Johnson Box in direct mail tradition) is the snippet of text that email clients show in the inbox view before a recipient opens the message. It appears after the sender name and subject line, typically in a lighter grey font.
Every major email client renders it differently:
- Gmail (desktop): Shows up to 90 characters after the subject line on the same row
- Apple Mail (iOS): Shows 2 lines of preview beneath the subject, roughly 75-100 characters
- Outlook (desktop): Shows a single preview line, around 35-55 characters
- Gmail (mobile): Shows approximately 30-55 characters depending on screen size
Because most opens now happen on mobile, the safe working length is 40-55 characters for guaranteed visibility, with up to 90 characters for clients that show more.
If you do not set a preheader explicitly, email clients read the first visible text in your HTML — which is frequently "View this email in your browser," your unsubscribe footer, or an ALT tag. These destroy open rates. Always set preheader text intentionally.
Why email preheaders matter for open rates
The inbox is a conversion funnel of its own. Before anyone reads your email, they decide whether to open it based on three signals: sender name, subject line, and preheader. Neglecting any one of them leaves open-rate points on the table.
- It extends the subject line's sell. A subject line has 6-10 words. The preheader doubles that real estate. Together they can set context, tease a benefit, and resolve urgency — things no subject line alone can do.
- It prevents embarrassing fallbacks. Without an intentional preheader, your first body text becomes the preview. "Hi [First Name]," or "ALT: hero-image" appearing in inboxes is common and immediately damages credibility.
- It directly lifts open rates. Optimised preheaders have driven open rate increases of 20-40% in documented split tests. A 1-percentage-point open rate improvement across 10,000 subscribers means 100 more opens per send.
- It works for every email type. Newsletters, promotional emails, transactional messages, drip sequences — every email benefits from a thoughtful preheader.
- It is almost zero extra work. Writing a good preheader takes under 5 minutes. The ROI per minute is higher than almost any other email optimization.
How email preheaders work technically
Preheader text is injected into the HTML of your email using a hidden span element placed immediately after the opening body tag, before any visible content. Most email service providers expose a dedicated "Preview text" field in their editor that handles this automatically.
<body>
<span style="display:none;max-height:0px;overflow:hidden;">
Your preheader text goes here — 40 to 90 characters
</span>
<!-- visible email content starts below -->
</body>
The hidden span is styled to be invisible in the email body but readable by inbox preview parsers. Some ESPs also add filler characters after the text to prevent the email body from bleeding into the preview.
Preheader strategies by email type
| Email type | Preheader goal | Example |
|---|---|---|
| Newsletter | Tease top story | "This week: why 90% of SEO audits miss the same thing" |
| Promotional | Extend the offer | "Ends midnight — get 30% off with code JULY30" |
| Abandoned cart | Create urgency | "Your cart expires in 24 hours. 3 items still inside." |
| Welcome email | Set expectations | "What to expect — and your first quick win, inside" |
| Transactional | Confirm action | "Order #4821 confirmed — estimated delivery: Thu 3 Jul" |
Real email preheader examples
Three before-and-after examples that show how a weak preheader becomes one that drives opens.
1. E-commerce promotional email
Weak preheader: View this email in your browser
Subject: Summer sale is here!
Strong preheader: 30% off everything — ends Sunday at midnight
2. B2B newsletter
Weak preheader: Hi [First Name], hope you're doing well...
Subject: The Weekly SEO Brief
Strong preheader: Google's core update winners — and the pattern behind them
3. SaaS abandoned trial email
Weak preheader: You haven't logged in yet
Subject: Don't lose your progress
Strong preheader: Your 14-day trial ends in 3 days — your data stays for 30 more
Email preheader vs subject line — how they work together
The subject line and preheader are two parts of the same open-rate argument. They should never repeat each other.
Subject line
- States the core hook or promise
- 6-10 words maximum for mobile
- Gets read first — sets the frame
- Optimise for curiosity or urgency
- Test emoji vs no-emoji for your list
Preheader
- Extends or adds a second angle
- 40-90 characters — more room to sell
- Read second — closes the argument
- Optimise for specificity and detail
- Add numbers, deadlines, social proof
6 best practices for email preheaders
- Never repeat the subject line. It wastes the real estate. The preheader should add new information — a deadline, a statistic, a secondary benefit.
- Front-load the key phrase. Mobile clients truncate at 30-55 characters. Put the word that matters most in the first 5 words.
- Use numbers whenever possible. "Save 30% — ends Sunday" outperforms "Big savings this weekend" every time. Numbers are specific; specificity earns trust.
- Match the email tone. A playful welcome email deserves a playful preheader. A transactional update needs a factual one. Mismatched tone confuses readers.
- A/B test every send you can. Split-test preheader variants at least once per quarter. Even a 2% open rate lift compounds substantially over a year.
- Include a filler block for long emails. Add invisible whitespace characters after your preheader to prevent body copy bleeding into the preview area.
The preheader is not a summary of the email. Summarising what is inside removes all reason to open. Use it to create forward momentum — give a hint, not the full picture. "3 things you're getting wrong about preheaders" beats "In this email: preheader tips" every time.
Common email preheader mistakes to avoid
- Leaving it blank — forces the client to pull random body text, frequently "View this email in your browser"
- Repeating the subject line verbatim — doubles the subject line word count in the preview but adds zero new value
- Writing more than 90 characters — extra text gets cut and you risk mid-sentence truncation
- Using vague language — "Great content inside!" tells the reader nothing and earns no opens
- Using spam trigger words — ALL CAPS or excessive exclamation marks in preheaders contribute to spam filter scoring
- Not testing across email clients — Gmail and Apple Mail render previews differently; use Litmus or Email on Acid before major sends
Frequently asked questions
An email preheader is the short text snippet shown next to or below the subject line in most email clients. It acts as a secondary subject line that gives recipients a second reason to open the email.
Keep preheaders between 40 and 90 characters. Mobile clients typically show 30-55 characters, while desktop clients show up to 90. Front-load the most important words so they survive truncation.
If no preheader is defined, most email clients pull the first readable text from the email body — often ALT text, navigation links, or "View this email in your browser", all of which hurt open rates.
Not directly. But a strong preheader lifts open rates, and higher open rates improve your sender reputation with ISPs over time, which indirectly improves deliverability.
Yes, and you should. Most major email platforms — Mailchimp, Klaviyo, HubSpot — allow A/B testing of preheader text independently of the subject line. Even small improvements compound across campaigns.
Related glossary terms
Sources
- [01]Mailchimp — Email preheader text best practices
- [02]Klaviyo — How to write preview text that improves open rates
- [03]Litmus — Ultimate guide to email preview text support across clients
- [04]Campaign Monitor — Subject line and preheader guide
- [05]Internal theStacc audit: open rate delta across 200 campaigns with and without preheader set — Q1 2026
