:class-selector
selector or pseudo-class · 17 supported, 2 partial, 1 unsupported across 21 clients
Client Support
| Client | Category | Engine | Support |
|---|---|---|---|
| Gmail | webmail | Gmail Web | Supported |
| Gmail Android | mobile | Gmail Mobile | Partial |
| Gmail iOS | mobile | Gmail Mobile | Partial |
| 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 | Unsupported |
| AOL Mail | webmail | AOL | Supported |
| Fastmail | webmail | Fastmail | Supported |
| Superhuman | desktop | Blink | Unknown |
Client-by-client behaviour for :class-selector
Fully supports :class-selector (17): Gmail, 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, AOL Mail, Fastmail.
Partial support (2): Gmail Android, Gmail iOS. Expect rendering quirks unique to each engine. Partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.
No support (1): Proton Mail. Plan fallbacks for these clients before relying on :class-selector in production sends.
Behaviour unverified in: Superhuman.
Fixes & Workarounds
Proton Mail
Unsupported":class-selector" is not supported in this email client.
Gmail Android
Partial":class-selector" is not supported in this email client.
Gmail iOS
Partial":class-selector" is not supported in this email client.
Related Features
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Try Emailens FreeSupport data last updated Apr 27, 2026 · synced from caniemail.com via @emailens/engine.