HTML Elements

<rp>

HTML element · 14 supported, 1 partial, 5 unsupported across 21 clients

The <rp> element provides parenthesis fallback for ruby annotations. It is rarely used outside East Asian typography contexts, and email client support is uneven. Production email targeting Japanese or Chinese audiences typically renders ruby manually using inline-block spans for greater control.

Client Support

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

Client-by-client behaviour for <rp>

Fully supports <rp> (14): Outlook 365, Outlook iOS, Outlook Android, Outlook for Mac, Apple Mail, Apple Mail iOS, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Samsung Mail, Thunderbird, Proton Mail, AOL Mail, Fastmail.

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

No support (5): Gmail, Gmail iOS, Outlook (New), Outlook Classic, HEY Mail. Plan fallbacks for these clients before relying on <rp> in production sends.

Behaviour unverified in: Superhuman.

When to use <rp> in email

Providing parenthetical pronunciation hints for ideograms in Japanese newsletters.
Ruby fallback in mixed-language brand emails.
Educational content in language-learning email products.

Rendering behaviour and edge cases

Most email clients ignore the semantic distinction between <rp> and surrounding ruby content.
Apple Mail respects <rp> visibility rules; other clients often render the parenthesis content inline as regular text.
Outlook on Windows shows <rp> content unconditionally, defeating its hide-when-ruby-supported purpose.

Recommended fallback strategy

If precise ruby rendering matters, build the ruby + parenthesis layout yourself with inline-block spans and explicit positioning. Avoid relying on browser-default ruby semantics in email.