Definition
The preheader (also called preview text or Johnson Box) is the short text snippet that appears after the subject line in most email clients. It is typically the first line of text from the email body, but you can set it explicitly. It is one of the most underutilised opportunities in email marketing.
Examples
Subject: "Your exclusive offer ends tomorrow" Preheader: "Use code SAVE30 at checkout — 30% off everything in your cart"
Why It Matters
The preheader is visible before the email is opened and is the second factor (after subject line) in the open decision. A well-written preheader can increase open rates by 10-30%.
Best Practices
- Always set it explicitly: If you do not, the email client grabs the first visible text — often "View in browser" or "Having trouble viewing?"
- Support the subject line: The preheader should extend or reinforce the subject line, not repeat it
- Keep it 85-100 characters: Most desktop clients show ~100 chars; mobile shows ~85
- Use it for urgency or value: Add a time-sensitive offer or key benefit
- Include emojis carefully: Some clients render emojis in preheaders, but test first
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Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
Above the Fold in Email
Above the fold in email refers to the content visible to a recipient before they scroll, a critical area for first impressions and primary calls to action.
AI Content Detection
AI content detection refers to the growing ability of email clients, spam filters and consumers to identify machine-generated email copy. It matters for deliverability, trust and engagement in an era of mass-produced AI marketing email.
AI Email Summary
An AI email summary is a short, machine-generated overview of an email's key points, shown by Gmail, Outlook and Apple Mail before a recipient opens the message. It is reshaping how email marketers think about subject lines, preview text and open rates.
AI-Generated Content in Email
AI-generated content in email is copy, images, code or subject lines produced by artificial intelligence tools to speed up campaign production and testing.
Frequently Asked Questions
Good practice here means handling Email Preheader in a way that is relevant, timely, and honest for your audience. Email preheader best practices cover how to use the preview text that appears after the subject line in most inboxes — a critical second line of messaging that can significantly boost open rates. Done well, it improves engagement and builds trust; done poorly, it creates friction that costs you results.
Because it touches the parts of email that drive outcomes: relevance, trust, and delivery. Small improvements compound, while repeated mistakes quietly erode the health of your programme.
The most common problems are treating Email Preheader as a one-off task, ignoring what the data says, and copying competitors without testing. All three lead to effort that does not translate into better results.
Compare the metrics it should influence — engagement, conversions, and deliverability — before and after you make changes. Trends over time matter far more than any single send.
It supports the same goal as the rest of your email programme: the right message to the right person at the right time. Aligned with segmentation and automation, it reinforces everything else rather than competing with it.