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Pseudo-Classes & Selectors

:grouping

selector or pseudo-class · 17 supported, 2 partial, 1 unsupported across 21 clients

17 of 21 email clients render :grouping fully (Sep 2, 2026 data); it breaks outright in Proton Mail.

  • 6/7 webmail, 5/6 desktop, 6/8 mobile clients support :grouping fully.
  • Unsupported in Proton Mail.
  • Partial in Gmail Android, Gmail iOS, behavior differs from browsers, test before relying on it.
  • 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 grouping (a, b, c) applies the same styles to multiple selectors at once. It is a CSS authoring convenience rather than a behavior , when <style> blocks are preserved, grouped selectors behave identically to writing them separately. Outlook strips <style>, so grouped selectors are inert there.

Client Support

ClientCategoryEngineSupport
GmailwebmailGmail WebSupported
Gmail AndroidmobileGmail MobilePartialSee caveat 1
Gmail iOSmobileGmail MobilePartialSee caveat 1
Outlook 365webmailOutlook WebSupported
Outlook (New)desktopOutlook WebSupported
Outlook ClassicdesktopMicrosoft WordSupported
Outlook iOSmobileOutlook MobileSupported
Outlook AndroidmobileOutlook MobileSupported
Outlook for MacdesktopWebKitSupported
Apple MaildesktopWebKitSupported
Apple Mail iOSmobileWebKitSupported
Yahoo MailwebmailYahooSupported
Yahoo Mail AndroidmobileYahooSupported
Yahoo Mail iOSmobileYahooSupported
Samsung MailmobileSamsungSupported
ThunderbirddesktopGeckoSupported
HEY MailwebmailWebKitSupported
Proton MailwebmailProtonUnsupported
AOL MailwebmailAOLSupported
FastmailwebmailFastmailSupported
SuperhumandesktopBlinkUnknown

Documented caveats (1)

  1. 1.Gmail Android, Gmail iOS: Partial. Not supported with non Google accounts.

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

Client-by-client behaviour for :grouping

Fully supports :grouping (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 :grouping in production sends.

Behaviour unverified in: Superhuman.

When to use :grouping in email

  • Applying a single base font-family rule to all text-bearing elements at once.
  • Resetting margin on multiple heading levels with one rule.
  • Sharing dark-mode color overrides across several distinct elements.

Rendering behaviour and edge cases

  • Grouping is purely syntactic , supported wherever each individual selector is supported.
  • Outlook ignores all <style>-based grouping.
  • Long groups can become hard to maintain , keep groups focused on a single styling concern.

Recommended fallback strategy

Use selector grouping freely in <style> blocks for cleanliness. For Outlook coverage, duplicate the grouped styles inline on each affected element.

Fixes & Workarounds

Proton Mail

Unsupported

":grouping" is not supported in this email client.

Gmail Android

Partial

":grouping" is not supported in this email client.

Gmail iOS

Partial

":grouping" is not supported in this email client.

Related Features

:adjacent-sibling :attribute-selector :chaining :checked :child-combinator :class-selector :descendant-combinator :first-child

Check your own HTML for :grouping

Paste your own, or run the sample below. Analyzed in this page, with no signup and nothing stored.
Zero-Friction Engine Preview

Test your :grouping layout across 21 email clients

Preview rendering, catch CSS issues, and see how :grouping displays across Outlook, Gmail, and Apple Mail. Free, no account needed.

Instant live preview · No signup required · 21 email engines

Last tested upstream: · Last synced by Emailens:

caniemail.com (MIT) records Oct 13, 2019 as the last time :grouping was tested in a real client, 6 years before this sync. Syncing copies that result forward, it does not re-test it. Carried in @emailens/engine data v0.12.2.