HTML element · data last changed 10 Nov 2026
<h1> in email clients
Works in 20 of 21. Untested in Superhuman.
caniemail (MIT) via @emailens/engine 0.18.22
No signup · Five clients free, Outlook Classic included · All 21 with an account
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<h1> is not among the 24 features we have screenshotted on real installs. The ones we have →
All 21 clients, problems first
| Client | Support |
|---|---|
| Superhuman | Untested |
Works in 20: Gmail, Gmail Android, Gmail iOS and 17 more. Show all
| Client | Support |
|---|---|
| Gmail | Works |
| Gmail Android | Works |
| Gmail iOS | Works |
| Outlook 365 | Works |
| Outlook (New) | Works |
| Outlook Classic | Works |
| Outlook iOS | Works |
| Outlook Android | Works |
| Outlook for Mac | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Yahoo Mail | Works |
| Yahoo Mail Android | Works |
| Yahoo Mail iOS | Works |
| Samsung Mail | Works |
| Thunderbird | Works |
| HEY Mail | Works |
| Proton Mail | Works |
| AOL Mail | Works |
| Fastmail | Works |
How <h1> behaves
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.
- Default font-size and margin vary widely between clients, explicitly set both inline.
- Outlook Classic 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.
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.
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