inert
CSS property · 3 supported, 0 partial, 14 unsupported across 21 clients
As of Sep 2, 2026, inert fails or degrades in 18 of 21 email clients, treat it as progressive enhancement, never structure.
- 0/7 webmail, 1/6 desktop, 2/8 mobile clients support inert fully.
- Unsupported in Gmail, Gmail Android, Gmail iOS, Outlook 365 and 10 more.
- Outlook Classic (Word engine, supported to at least 2029) does not fully support inert, 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 Apr 16, 2026, 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 | Unsupported |
| Outlook (New) | desktop | Outlook Web | Unsupported |
| Outlook Classic | desktop | Microsoft Word | Unsupported |
| Outlook iOS | mobile | Outlook Mobile | Unsupported |
| Outlook Android | mobile | Outlook Mobile | Unsupported |
| Outlook for Mac | desktop | WebKit | Unsupported |
| Apple Mail | desktop | WebKit | Supported |
| Apple Mail iOS | mobile | WebKit | Supported |
| Yahoo Mail | webmail | Yahoo | Unsupported |
| Yahoo Mail Android | mobile | Yahoo | Unsupported |
| Yahoo Mail iOS | mobile | Yahoo | Unsupported |
| Samsung Mail | mobile | Samsung | Supported |
| Thunderbird | desktop | Gecko | Unknown |
| HEY Mail | webmail | WebKit | Unknown |
| Proton Mail | webmail | Proton | Unsupported |
| AOL Mail | webmail | AOL | Unsupported |
| Fastmail | webmail | Fastmail | Unknown |
| Superhuman | desktop | Blink | Unknown |
Client-by-client behaviour for inert
Fully supports inert (3): Apple Mail, Apple Mail iOS, Samsung Mail.
No support (14): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook (New), Outlook Classic, Outlook iOS, Outlook Android, Outlook for Mac, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Proton Mail, AOL Mail. Plan fallbacks for these clients before relying on inert in production sends.
Behaviour unverified in: Thunderbird, HEY Mail, Fastmail, Superhuman.
Fixes & Workarounds
Gmail
Unsupported"inert" is not supported in this email client.
Gmail Android
Unsupported"inert" is not supported in this email client.
Gmail iOS
Unsupported"inert" is not supported in this email client.
Outlook 365
Unsupported"inert" is not supported in this email client.
Outlook (New)
Unsupported"inert" is not supported in this email client.
Outlook Classic
Unsupported"inert" is not supported in this email client.
Outlook iOS
Unsupported"inert" is not supported in this email client.
Outlook Android
Unsupported"inert" is not supported in this email client.
Outlook for Mac
Unsupported"inert" is not supported in this email client.
Yahoo Mail
Unsupported"inert" is not supported in this email client.
Yahoo Mail Android
Unsupported"inert" is not supported in this email client.
Yahoo Mail iOS
Unsupported"inert" is not supported in this email client.
Proton Mail
Unsupported"inert" is not supported in this email client.
AOL Mail
Unsupported"inert" is not supported in this email client.
Related Features
Check your own HTML for inert
Paste your own, or run the sample below. Analyzed in this page, with no signup and nothing stored.
Test your inert layout across 21 email clients
Preview rendering, catch CSS issues, and see how inert 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 Apr 16, 2026 as the last time inert was tested in a real client, less than a year before this sync. Syncing copies that result forward, it does not re-test it. Carried in @emailens/engine data v0.12.2.