Pseudo-Classes & Selectors

:chaining

selector or pseudo-class · 14 supported, 2 partial, 4 unsupported across 21 clients

14 of 21 email clients render :chaining fully (Sep 2, 2026 data); it breaks outright in Outlook 365, Outlook (New), Outlook Classic and 1 more.

5/7 webmail, 3/6 desktop, 6/8 mobile clients support :chaining fully.
Unsupported in Outlook 365, Outlook (New), Outlook Classic, Proton Mail.
Partial in Gmail Android, Gmail iOS, behavior differs from browsers, test before relying on it.
Outlook Classic (Word engine, supported to at least 2029) does not fully support :chaining, and its replacement changes little here; see the deprecation diff.
Across all clients, only 6 of 298 tracked HTML/CSS features render identically everywhere.

Source: caniemail.com (MIT), via the Emailens engine. Last tested upstream Oct 13, 2019, synced by Emailens Sep 2, 2026.

Selector chaining (combining classes or tags without a separator, e.g., .button.primary) increases specificity by requiring multiple conditions on the same element. In email, chained selectors live in <style> blocks and only apply where <style> is preserved.

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Supported
Gmail Android	mobile	Gmail Mobile	Partial^{See caveat 1}
Gmail iOS	mobile	Gmail Mobile	Partial^{See caveat 1}
Outlook 365	webmail	Outlook Web	Unsupported^{See caveat 2}
Outlook (New)	desktop	Outlook Web	Unsupported^{See caveat 3}
Outlook Classic	desktop	Microsoft Word	Unsupported^{See caveat 3}
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

Documented caveats (3)

1.Gmail Android, Gmail iOS: Partial. Not supported with non Google accounts.
2.Outlook 365: Buggy. Only the first selector of the chain is prefixed in the styles, but all classes are prefixed in the HTML.
3.Outlook (New), Outlook Classic: Buggy. Styles will be applied to the first selector of the chain.

Caveats recorded by caniemail.com (MIT) and carried verbatim, one entry per wording rather than per client.

Client-by-client behaviour for :chaining

Fully supports :chaining (14): Gmail, 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 (4): Outlook 365, Outlook (New), Outlook Classic, Proton Mail. Plan fallbacks for these clients before relying on :chaining in production sends.

Behaviour unverified in: Superhuman.

When to use :chaining in email

Targeting a class only when combined with another modifier class.
Increasing specificity to override a default rule without using !important.
Constraining styles to elements with both a tag and class match.

Rendering behaviour and edge cases

Outlook strips <style>, so chained selectors do not apply there.
Gmail's class-rewriting can break selectors that depend on multiple class names matching.
Specificity from chaining is additive , a chained selector outranks a single class.

Recommended fallback strategy

Use chained selectors in <style> blocks for progressive enhancement only. For Outlook compatibility, inline the equivalent styles on the matching elements directly.