HTML Elements

<base>

HTML element · 5 supported, 7 partial, 2 unsupported across 15 clients

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Partial
Gmail Android	mobile	Gmail Mobile	Partial
Gmail iOS	mobile	Gmail Mobile	Partial
Outlook 365	webmail	Outlook Web	Partial
Outlook (New)	desktop	Outlook Web	Supported
Outlook Classic	desktop	Microsoft Word	Unsupported
Outlook iOS	mobile	Outlook Mobile	Partial
Outlook Android	mobile	Outlook Mobile	Unsupported
Apple Mail	desktop	WebKit	Supported
Apple Mail iOS	mobile	WebKit	Supported
Yahoo Mail	webmail	Yahoo	Partial
Samsung Mail	mobile	Samsung	Supported
Thunderbird	desktop	Gecko	Supported
HEY Mail	webmail	WebKit	Partial
Superhuman	desktop	Blink	Unknown

Client-by-client behaviour for <base>

Fully supports <base> (5): Outlook (New), Apple Mail, Apple Mail iOS, Samsung Mail, Thunderbird.

Partial support (7): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook iOS, Yahoo Mail, HEY 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 (2): Outlook Classic, Outlook Android. Plan fallbacks for these clients before relying on <base> in production sends.

Behaviour unverified in: Superhuman.