:only-child
selector or pseudo-class · 13 supported, 1 partial, 6 unsupported across 21 clients
13 of 21 email clients render :only-child fully (Sep 2, 2026 data); it breaks outright in Gmail, Gmail Android, Gmail iOS and 3 more.
- 4/7 webmail, 3/6 desktop, 6/8 mobile clients support :only-child fully.
- Unsupported in Gmail, Gmail Android, Gmail iOS, Outlook (New) and 2 more.
- Partial in Outlook 365, behavior differs from browsers, test before relying on it.
- Outlook Classic (Word engine, supported to at least 2029) does not fully support :only-child, 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 19, 2019, synced by Emailens Sep 2, 2026.
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 | PartialSee caveat 1 |
| Outlook (New) | desktop | Outlook Web | Unsupported |
| Outlook Classic | desktop | Microsoft Word | Unsupported |
| 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 (1)
- 1.Outlook 365: Partial. Only supported on type selectors.
Caveats recorded by caniemail.com (MIT) and carried verbatim, one entry per wording rather than per client.
Client-by-client behaviour for :only-child
Fully supports :only-child (13): 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 (1): Outlook 365. Expect rendering quirks unique to each engine. Partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.
No support (6): Gmail, Gmail Android, Gmail iOS, Outlook (New), Outlook Classic, Proton Mail. Plan fallbacks for these clients before relying on :only-child in production sends.
Behaviour unverified in: Superhuman.
Fixes & Workarounds
Gmail
Unsupported":only-child" is not supported in this email client.
Gmail Android
Unsupported":only-child" is not supported in this email client.
Gmail iOS
Unsupported":only-child" is not supported in this email client.
Outlook (New)
Unsupported":only-child" is not supported in this email client.
Outlook Classic
Unsupported":only-child" is not supported in this email client.
Proton Mail
Unsupported":only-child" is not supported in this email client.
Outlook 365
Partial":only-child" is not supported in this email client.
Related Features
Check your own HTML for :only-child
Paste your own, or run the sample below. Analyzed in this page, with no signup and nothing stored.
Test your :only-child layout across 21 email clients
Preview rendering, catch CSS issues, and see how :only-child 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 19, 2019 as the last time :only-child 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.