CSS Functions

max

CSS function · 7 supported, 3 partial, 10 unsupported across 21 clients

As of Sep 2, 2026, max fails or degrades in 14 of 21 email clients, treat it as progressive enhancement, never structure.

3/7 webmail, 3/6 desktop, 1/8 mobile clients support max fully.
Unsupported in Outlook 365, Outlook (New), Outlook Classic, Outlook iOS and 6 more.
Partial in Gmail Android, Gmail iOS, Samsung Mail, behavior differs from browsers, test before relying on it.
Outlook Classic (Word engine, supported to at least 2029) does not fully support max, 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 7, 2021, synced by Emailens Sep 2, 2026.

The max() CSS function returns the largest of a set of values and is used to enforce a minimum. Like min() and calc(), it is a modern function with limited email support , Outlook on Windows ignores it, while Apple Mail and modern Gmail honor it.

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Supported
Gmail Android	mobile	Gmail Mobile	Partial^{See caveat 1}
Gmail iOS	mobile	Gmail Mobile	Partial^{See caveat 1}
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	Supported
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	Partial^{See caveat 2}
Thunderbird	desktop	Gecko	Supported
HEY Mail	webmail	WebKit	Supported
Proton Mail	webmail	Proton	Supported
AOL Mail	webmail	AOL	Unsupported
Fastmail	webmail	Fastmail	Unsupported
Superhuman	desktop	Blink	Unknown

Documented caveats (2)

1.Gmail Android, Gmail iOS: Partial. Not supported with non Google accounts.
2.Samsung Mail: Partial. Not supported with Microsoft accounts.

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

Client-by-client behaviour for max

Fully supports max (7): Gmail, Outlook for Mac, Apple Mail, Apple Mail iOS, Thunderbird, HEY Mail, Proton Mail.

Partial support (3): Gmail Android, Gmail iOS, Samsung 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 (10): Outlook 365, Outlook (New), Outlook Classic, Outlook iOS, Outlook Android, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, AOL Mail, Fastmail. Plan fallbacks for these clients before relying on max in production sends.

Behaviour unverified in: Superhuman.

When to use max in email

Enforcing a minimum padding regardless of fluid container size.
Ensuring a minimum font-size in fluid typography systems.
Forcing a minimum width on responsive button elements to keep them tappable on small screens.

Rendering behaviour and edge cases

Outlook on Windows ignores max() and falls back to the previous declaration.
Apple Mail supports max() across recent macOS and iOS releases.
max() expressions with mixed units behave inconsistently , prefer same-unit comparisons.

Recommended fallback strategy

Always supply a literal fallback before max() so Outlook receives a sensible default. Use max() as progressive enhancement layered on top of conservative pixel values.