HTML & Email Structure

amp4email

CSS property · 6 supported, 0 partial, 14 unsupported across 21 clients

As of Sep 2, 2026, amp4email fails or degrades in 15 of 21 email clients, treat it as progressive enhancement, never structure.

2/7 webmail, 0/6 desktop, 4/8 mobile clients support amp4email fully.
Unsupported in Outlook 365, Outlook (New), Outlook Classic, Outlook iOS and 10 more.
Outlook Classic (Word engine, supported to at least 2029) does not fully support amp4email, 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 Mar 31, 2020, synced by Emailens Sep 2, 2026.

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Supported^{See caveat 1}
Gmail Android	mobile	Gmail Mobile	Supported
Gmail iOS	mobile	Gmail Mobile	Supported
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	Unsupported
Apple Mail iOS	mobile	WebKit	Unsupported
Yahoo Mail	webmail	Yahoo	Supported^{See caveat 1}
Yahoo Mail Android	mobile	Yahoo	Supported
Yahoo Mail iOS	mobile	Yahoo	Supported
Samsung Mail	mobile	Samsung	Unsupported
Thunderbird	desktop	Gecko	Unsupported
HEY Mail	webmail	WebKit	Unsupported
Proton Mail	webmail	Proton	Unsupported
AOL Mail	webmail	AOL	Unsupported
Fastmail	webmail	Fastmail	Unsupported
Superhuman	desktop	Blink	Unknown

Documented caveats (1)

1.Gmail, Yahoo Mail: Supported on compatible browsers. Refer to ‘supported platforms’ links listed below under resources.

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

Client-by-client behaviour for amp4email

Fully supports amp4email (6): Gmail, Gmail Android, Gmail iOS, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS.

No support (14): Outlook 365, Outlook (New), Outlook Classic, Outlook iOS, Outlook Android, Outlook for Mac, Apple Mail, Apple Mail iOS, Samsung Mail, Thunderbird, HEY Mail, Proton Mail, AOL Mail, Fastmail. Plan fallbacks for these clients before relying on amp4email in production sends.

Behaviour unverified in: Superhuman.