CSS Properties

resize

CSS property · 1 supported, 1 partial, 16 unsupported across 21 clients

As of Sep 2, 2026, resize fails or degrades in 20 of 21 email clients, treat it as progressive enhancement, never structure.

0/7 webmail, 0/6 desktop, 1/8 mobile clients support resize fully.
Unsupported in Gmail, Gmail Android, Gmail iOS, Outlook 365 and 12 more.
Partial in Apple Mail, behavior differs from browsers, test before relying on it.
Outlook Classic (Word engine, supported to at least 2029) does not fully support resize, 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 Jan 17, 2024, synced by Emailens Sep 2, 2026.

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Unsupported^{See caveat 1}
Gmail Android	mobile	Gmail Mobile	Unsupported
Gmail iOS	mobile	Gmail Mobile	Unsupported^{See caveat 1}
Outlook 365	webmail	Outlook Web	Unsupported^{See caveat 1}
Outlook (New)	desktop	Outlook Web	Unsupported
Outlook Classic	desktop	Microsoft Word	Unsupported
Outlook iOS	mobile	Outlook Mobile	Unsupported^{See caveat 1}
Outlook Android	mobile	Outlook Mobile	Unsupported
Outlook for Mac	desktop	WebKit	Unsupported^{See caveat 1}
Apple Mail	desktop	WebKit	Partial^{See caveat 2}
Apple Mail iOS	mobile	WebKit	Unsupported
Yahoo Mail	webmail	Yahoo	Unsupported^{See caveat 1}
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^{See caveat 1}
Fastmail	webmail	Fastmail	Unknown
Superhuman	desktop	Blink	Unsupported

Documented caveats (2)

1.Gmail, Gmail iOS, Outlook 365, Outlook iOS, Outlook for Mac, Yahoo Mail, AOL Mail: resize property is stripped from style tag
2.Apple Mail: Does not support inline and block values

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

Client-by-client behaviour for resize

Fully supports resize (1): Samsung Mail.

Partial support (1): Apple Mail. Expect rendering quirks unique to each engine. Partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.

No support (16): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook (New), Outlook Classic, Outlook iOS, Outlook Android, Outlook for Mac, Apple Mail iOS, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Proton Mail, AOL Mail, Superhuman. Plan fallbacks for these clients before relying on resize in production sends.

Behaviour unverified in: Thunderbird, HEY Mail, Fastmail.