Pseudo-Classes & Selectors

:attribute-selector

selector or pseudo-class · 5 supported, 7 partial, 2 unsupported across 15 clients

Attribute selectors target elements based on their attributes (e.g., [type=email], [data-id="123"]). Email support is limited because many clients strip <style> blocks where these selectors live. When <style> blocks are preserved, attribute selectors work in modern clients but are ignored in Outlook on Windows.

Client Support

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

Client-by-client behaviour for :attribute-selector

Fully supports :attribute-selector (5): Apple Mail, Apple Mail iOS, Samsung Mail, Thunderbird, HEY Mail.

Partial support (7): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook iOS, Outlook Android, Yahoo Mail. Expect rendering quirks unique to each engine — partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.

No support (2): Outlook (New), Outlook Classic. Plan fallbacks for these clients before relying on :attribute-selector in production sends.

Behaviour unverified in: Superhuman.

When to use :attribute-selector in email

Targeting form inputs by type in AMP for Email contexts.
Selecting elements by data-* attributes for dark-mode style overrides.
Cross-cutting styles based on aria-* attributes for accessibility consistency.

Rendering behaviour and edge cases

Outlook strips <style> blocks, neutralizing attribute selectors.
Gmail rewrites class names but preserves attribute selectors when <style> blocks survive.
Apple Mail honors attribute selectors reliably across recent macOS and iOS releases.

Recommended fallback strategy

Use attribute selectors only when <style> blocks are preserved. For Outlook coverage, duplicate the styling inline on the matching elements. Treat attribute-based selectors as progressive enhancement, never as the only path to a critical style.