<h1>
HTML element · 14 supported, 0 partial, 0 unsupported across 15 clients
The <h1> element marks the primary heading of a document and is supported by every email client. Default browser styling for <h1> is large and bold with significant top and bottom margin, which is rarely what email designs intend. Always reset <h1> styling inline to prevent client-default spacing from disrupting the layout.
Client Support
| Client | Category | Engine | Support |
|---|---|---|---|
| Gmail | webmail | Gmail Web | Supported |
| Gmail Android | mobile | Gmail Mobile | Supported |
| Gmail iOS | mobile | Gmail Mobile | Supported |
| Outlook 365 | webmail | Outlook Web | Supported |
| Outlook (New) | desktop | Outlook Web | Supported |
| Outlook Classic | desktop | Microsoft Word | Supported |
| Outlook iOS | mobile | Outlook Mobile | Supported |
| Outlook Android | mobile | Outlook Mobile | Supported |
| Apple Mail | desktop | WebKit | Supported |
| Apple Mail iOS | mobile | WebKit | Supported |
| Yahoo Mail | webmail | Yahoo | Supported |
| Samsung Mail | mobile | Samsung | Supported |
| Thunderbird | desktop | Gecko | Supported |
| HEY Mail | webmail | WebKit | Supported |
| Superhuman | desktop | Blink | Unknown |
Client-by-client behaviour for <h1>
Fully supports <h1> (14): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook (New), Outlook Classic, Outlook iOS, Outlook Android, Apple Mail, Apple Mail iOS, Yahoo Mail, Samsung Mail, Thunderbird, HEY Mail.
Behaviour unverified in: Superhuman.
When to use <h1> in email
- The headline of a marketing email's hero section.
- Major section titles in long-form newsletter content.
- Article-style transactional confirmations with a clear primary message.
Rendering behaviour and edge cases
- Default font-size and margin vary widely between clients — explicitly set both inline.
- Outlook on Windows respects <h1> styling but inherits Word-style typography that may surprise web developers.
- Some clients down-rank <h1> in dark mode, applying their own contrast adjustments.
Recommended fallback strategy
Override default <h1> styling with explicit inline font-size, font-weight, line-height, and margin. Treat the inline declaration as authoritative — do not rely on client defaults for a hero headline.
Related Features
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Try Emailens FreeSupport data last updated Apr 27, 2026 · synced from caniemail.com via @emailens/engine.