Pseudo-Classes & Selectors

:has

selector or pseudo-class · 6 supported, 0 partial, 14 unsupported across 21 clients

The :has pseudo-class selects elements that contain a descendant matching a sub-selector. It is one of the newest CSS features and email support is limited , Apple Mail and modern Gmail support it in modern engine versions, while Outlook and most others ignore it. It is best treated as progressive enhancement.

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Unsupported
Gmail Android	mobile	Gmail Mobile	Unsupported
Gmail iOS	mobile	Gmail Mobile	Unsupported
Outlook 365	webmail	Outlook Web	Unsupported
Outlook (New)	desktop	Outlook Web	Unsupported
Outlook Classic	desktop	Microsoft Word	Unsupported
Outlook iOS	mobile	Outlook Mobile	Unsupported
Outlook Android	mobile	Outlook Mobile	Unsupported
Outlook for Mac	desktop	WebKit	Unsupported
Apple Mail	desktop	WebKit	Supported
Apple Mail iOS	mobile	WebKit	Supported
Yahoo Mail	webmail	Yahoo	Unsupported
Yahoo Mail Android	mobile	Yahoo	Unsupported
Yahoo Mail iOS	mobile	Yahoo	Unsupported
Samsung Mail	mobile	Samsung	Supported
Thunderbird	desktop	Gecko	Unsupported
HEY Mail	webmail	WebKit	Supported
Proton Mail	webmail	Proton	Supported
AOL Mail	webmail	AOL	Unsupported
Fastmail	webmail	Fastmail	Supported
Superhuman	desktop	Blink	Unknown

Client-by-client behaviour for :has

Fully supports :has (6): Apple Mail, Apple Mail iOS, Samsung Mail, HEY Mail, Proton Mail, Fastmail.

No support (14): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook (New), Outlook Classic, Outlook iOS, Outlook Android, Outlook for Mac, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Thunderbird, AOL Mail. Plan fallbacks for these clients before relying on :has in production sends.

Behaviour unverified in: Superhuman.

When to use :has in email

Styling cards differently when they contain an image versus text-only content.
Adjusting list item spacing based on whether a parent contains nested lists.
Conditional styling in modern-client-targeted designs.

Rendering behaviour and edge cases

Outlook on Windows ignores :has entirely.
Apple Mail supports :has on macOS Ventura+ and iOS 16+.
Gmail Web honors :has only when <style> blocks survive sanitization.

Recommended fallback strategy

Provide a default styling that works without :has, then use :has selectors for refinements. Never rely on :has to deliver structural visibility , fall back to explicit class-based styling as the baseline.