Definition
A preview line, or preheader, is the snippet shown after the subject in most inboxes. It works as a second subject line and lifts open rates.
It should complement the subject and front-load the most valuable words.
The preview line is a second subject line that drives opens, so it deserves real attention. It should complement the subject and front-load value. With AI inboxes, it also feeds machine summaries.
Writing Preview Lines
Keep the preview under 100 characters.
Complement, not repeat, the subject.
Why It Matters
The preview line is a second subject line that drives opens. Understanding it is a cheap way to lift performance.
Best Practices
- Keep the preview under 100 characters.
- Complement, not repeat, the subject.
- Start with the most valuable words first.
- End with a hint of what follows.
- Test preview variations.
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Related Glossary Terms
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.
Accessible CTA (Email)
An accessible CTA is a button or link coded with sufficient colour contrast, visible focus states, descriptive screen-reader text, and a minimum touch target of 44×44 pixels.
Adaptive Design
Adaptive design in email uses predefined layouts that adjust to specific device or client widths, rather than fluidly resizing to every possible screen.
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-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.
AIDA Model for Email
The AIDA model (Attention, Interest, Desire, Action) is a classic copywriting framework used to structure email campaigns that guide subscribers from awareness to conversion.
Frequently Asked Questions
The inbox snippet that appears with the subject. The preview line is a second subject line that drives opens, so it deserves real attention.
Aim under 100 characters for mobile and desktop. It should complement the subject and front-load value.
Yes, it wastes prime hook space. With AI inboxes, it also feeds machine summaries.
No, it should complement it. The preview line is a second subject line that drives opens, so it deserves real attention.
Yes, AI summaries draw from it. It should complement the subject and front-load value.