Selector or pseudo-class · data last changed 10 Nov 2026

:attribute-selector in email clients

Works in 6 of 21. Not supported in Outlook Classic and Proton Mail. Partial in Gmail, Gmail Android, Gmail iOS and 9 more. Untested in Superhuman.

Your reader in Outlook Classic sees the email without :attribute-selector, even if it looks right where you tested it.

caniemail (MIT) via @emailens/engine 0.18.22

What to do instead in Outlook Classic

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.

There is no drop-in fix for :attribute-selector in Outlook Classic. Design so the email still reads without it.

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:attribute-selector is not among the 24 features we have screenshotted on real installs. The ones we have →

All 21 clients, problems first

Client	Support
Outlook Classic	Not supported
Proton Mail	Not supported
Gmail	Partial ^{See caveat 1}
Gmail Android	Partial ^{See caveat 2}
Gmail iOS	Partial ^{See caveat 2}
Outlook 365	Partial ^{See caveat 3}
Outlook (New)	Partial ^{See caveat 3}
Outlook iOS	Partial ^{See caveat 4}
Outlook Android	Partial ^{See caveat 4}
Outlook for Mac	Partial ^{See caveat 3}
Yahoo Mail	Partial ^{See caveat 5}
Yahoo Mail Android	Partial ^{See caveat 5}
Yahoo Mail iOS	Partial ^{See caveat 5}
AOL Mail	Partial ^{See caveat 5}
Superhuman	Untested

Works in 6: Apple Mail, Apple Mail iOS, Samsung Mail and 3 more. Show all

Client	Support
Apple Mail	Works
Apple Mail iOS	Works
Samsung Mail	Works
Thunderbird	Works
HEY Mail	Works
Fastmail	Works

Caveats (5)

1. Gmail: Partial. Only supports [attr~=value] syntax. Only class as an attribute name is known to be supported.
2. Gmail Android, Gmail iOS: Partial. Only supports [attr~=value] syntax. Only class as an attribute name is known to be supported. Partial. Doesn't work with non Google accounts.
3. Outlook 365, Outlook (New), Outlook for Mac: Partial. Can not be used with a class selector (.test[class]). Must be used solo ([class]) or with an element selector (td[class]). Partial. Only supports [attr], [attr=value], [attr~=value], [attr|=value] syntaxes. Buggy. A class="test" in the HTML is prefixed class="x_test", but an attribute selector stays unprefixed [class="test"].
4. Outlook iOS, Outlook Android: Partial. Can not be used with a class selector (.test[class]). Must be used solo ([class]) or with an element selector (td[class]). Partial. Only supports [attr], [attr=value], [attr~=value], [attr|=value] syntaxes.
5. Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, AOL Mail: Partial. Only supports [attr=value] syntax.

Caveats as recorded by caniemail (MIT), one entry per wording.

How :attribute-selector behaves

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 Classic.

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.

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