<h1>
HTML element · 20 supported, 0 partial, 0 unsupported across 21 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 |
| Outlook for Mac | desktop | WebKit | Supported |
| Apple Mail | desktop | WebKit | Supported |
| Apple Mail iOS | mobile | WebKit | Supported |
| Yahoo Mail | webmail | Yahoo | Supported |
| Yahoo Mail Android | mobile | Yahoo | Supported |
| Yahoo Mail iOS | mobile | Yahoo | Supported |
| Samsung Mail | mobile | Samsung | Supported |
| Thunderbird | desktop | Gecko | Supported |
| HEY Mail | webmail | WebKit | Supported |
| Proton Mail | webmail | Proton | Supported |
| AOL Mail | webmail | AOL | Supported |
| Fastmail | webmail | Fastmail | Supported |
| Superhuman | desktop | Blink | Unknown |
Client-by-client behaviour for <h1>
Fully supports <h1> (20): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook (New), Outlook Classic, Outlook iOS, Outlook Android, Outlook for Mac, Apple Mail, Apple Mail iOS, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Samsung Mail, Thunderbird, HEY Mail, Proton Mail, AOL Mail, Fastmail.
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.