z-index
CSS property · 16 supported, 0 partial, 5 unsupported across 21 clients
16 of 21 email clients render z-index fully (Sep 2, 2026 data); it breaks outright in Gmail, Gmail Android, Gmail iOS and 2 more.
- 6/7 webmail, 4/6 desktop, 6/8 mobile clients support z-index fully.
- Unsupported in Gmail, Gmail Android, Gmail iOS, Outlook (New) and 1 more.
- Outlook Classic (Word engine, supported to at least 2029) does not fully support z-index, 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 May 16, 2021, 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 | Supported |
| 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 | Supported |
| AOL Mail | webmail | AOL | Supported |
| Fastmail | webmail | Fastmail | Supported |
| Superhuman | desktop | Blink | Supported |
Client-by-client behaviour for z-index
Fully supports z-index (16): Outlook 365, 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, Proton Mail, AOL Mail, Fastmail, Superhuman.
No support (5): Gmail, Gmail Android, Gmail iOS, Outlook (New), Outlook Classic. Plan fallbacks for these clients before relying on z-index in production sends.
Fixes & Workarounds
Gmail
Unsupported"z-index" is not supported in this email client.
Gmail Android
Unsupported"z-index" is not supported in this email client.
Gmail iOS
Unsupported"z-index" is not supported in this email client.
Outlook (New)
Unsupported"z-index" is not supported in this email client.
Outlook Classic
Unsupported"z-index" is not supported in this email client.
Related Features
Check your own HTML for z-index
Paste your own, or run the sample below. Analyzed in this page, with no signup and nothing stored.
Test your z-index layout across 21 email clients
Preview rendering, catch CSS issues, and see how z-index 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 May 16, 2021 as the last time z-index was tested in a real client, 5 years before this sync. Syncing copies that result forward, it does not re-test it. Carried in @emailens/engine data v0.12.2.