Email Preheader Best Practices

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.

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

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%.