Definition
Preview text (also called preheader or Johnson box) is the short summary text that appears next to or below the subject line in most email clients before the recipient opens the message. While basic preview text optimisation focuses on simply including it, advanced optimisation addresses the significant variations in how different email clients render the text, the creative opportunities for brand reinforcement, and systematic A/B testing methodology. Litmus research indicates that 24-47% of email recipients (depending on client) make their open decision based on preview text combined with the subject line, making it one of the most impactful elements for open rate optimisation.
The technical complexity of preview text stems from the wide variation in character display limits across email clients. Gmail's mobile app displays approximately 35-50 characters, Apple Mail shows 50-70 characters, Outlook varies from 50-85 characters, and Yahoo shows 60-75 characters. Some clients, particularly older mobile clients, limit to as few as 25-30 characters. The most important content must therefore appear in the first 20-30 characters to ensure it is visible everywhere. Advanced techniques include using ASCII art to create visual brand elements in the preview text — simple patterns that reinforce brand recognition in the inbox. Emoji usage in preview text has been shown to increase open rates by 2-5% in controlled tests, though the effect varies dramatically by audience and brand context. The strategic choice between teaser approaches (hinting at content to create curiosity) vs description approaches (clearly stating what the email contains) depends on audience familiarity and the campaign objective.
Best Practices
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Place the most critical preview text content within the first 30 characters. This ensures visibility across all email clients including those with the shortest character limits. Structure preview text as an inverted pyramid — most important information first, supplementary detail after. Test your preview text in at least 10 different email clients before deployment.
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Implement systematic A/B testing for preview text alongside subject line testing. Run factorial tests that vary subject line and preview text simultaneously to detect interaction effects. A subject line that pairs well with one preview text may underperform with another. Use a minimum sample size of 10,000 per variant and run tests for at least 48 hours.
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Test emoji usage in preview text with caution and audience awareness. Emoji in preview text can increase open rates by 2-5% for B2C audiences in casual contexts. For B2B or formal audiences, emoji can decrease open rates by 5-10%. Test emoji on a subset of your list before full deployment. Avoid emoji that may render differently across devices or hold unintended meanings.
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Use preview text for brand reinforcement in addition to content description. Include the brand name, a branded hashtag, or a distinctive brand phrase within the first 50 characters. For recognised brands, this increases trust in the inbox and improves open rates. For lesser-known brands, brand mentions in preview text may reduce curiosity — test brand vs content-only preview text.
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Choose between teaser and description approaches based on audience engagement level. Teaser preview text (creating curiosity without revealing content) works better for highly engaged segments with established trust. Description preview text (clearly stating content or value) works better for less engaged segments or cold audiences. Segment your test by engagement level to identify the optimal approach.
Related Glossary Terms
Control Group
Control or holdout group testing withholds a random subscriber segment from a campaign to measure incremental lift in engagement, revenue, and conversion.
Dark Mode
Dark mode in email refers to how email clients render messages when the recipient has dark mode enabled. It affects colour display, image rendering, and readability. Designers use CSS media queries and hybrid coding techniques to control the dark mode appearance.
Email Accessibility
Email accessibility ensures marketing emails are usable by people with disabilities, including those using screen readers, keyboard navigation, or assistive technologies. It follows WCAG 2.1 guidelines for structure, contrast, semantics, and descriptive content.
Email Brand Guidelines
Email brand guidelines document the specific rules for logo usage, colour palette, typography, tone of voice, and component specifications across all email communications.
Email Branding
The consistent use of visual identity, tone of voice, and design elements across email communications to build instant recognition and trust in the inbox.
Email Conversion Optimisation
Conversion rate optimisation (CRO) specifically for email traffic focuses on landing page alignment, CTA testing, and friction reduction to maximise email click-through conversion.
Frequently Asked Questions
Write 85-100 characters to ensure the full message is visible across all clients, but place the most critical information in the first 25-30 characters. Longer preview text will be truncated differently across clients — the key is ensuring the truncation point does not cut off essential information.
Preview text itself does not directly affect spam filters, but deceptive preview text — claiming content that does not exist in the email — can contribute to spam classification and violates best practices. Preview text should accurately reflect email content and should not use misleading keywords or excessive punctuation.
Complement, never repeat. Preview text should add new information that builds on the subject line rather than restating it. The subject line and preview text together should form a complete, compelling inbox proposition. Repeating the subject line wastes the preview text's opportunity to provide additional context.
ASCII art uses text characters to create simple visual patterns in preview text, such as arrows (>>>), dividers (====), stars (**), or brand shapes. These visual elements can draw attention in the inbox and reinforce brand recognition. Use sparingly and test to ensure they render correctly across email clients.
Preview text is commonly "hidden" by placing it immediately after the opening body tag and before the main content, then using CSS to hide it. The standard technique uses inline styles with display:none or font-size:0 combined with max-height:0 and overflow:hidden. Test hidden preview text rendering across major email clients before deployment.