HTML element · data last changed 10 Nov 2026
<rt> in email clients
Works in 15 of 21. Not supported in Gmail, Gmail iOS, Outlook Classic and 1 more. Partial in Gmail Android. Untested in Superhuman.
Your reader in Outlook Classic sees the email without <rt>, even if it looks right where you tested it.
caniemail (MIT) via @emailens/engine 0.18.22
What to do instead in Outlook Classic
For mission-critical ruby, render the annotation as inline-block text positioned above the base using explicit margin/font-size, rather than relying on the <ruby>/<rt> default rendering.
There is no drop-in fix for <rt> in Outlook Classic. Design so the email still reads without it.
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<rt> is not among the 24 features we have screenshotted on real installs. The ones we have →
All 21 clients, problems first
| Client | Support |
|---|---|
| Gmail | Not supported |
| Gmail iOS | Not supported |
| Outlook Classic | Not supported |
| HEY Mail | Not supported |
| Gmail Android | Partial See caveat 1 |
| Superhuman | Untested |
Works in 15: Outlook 365, Outlook (New), Outlook iOS and 12 more. Show all
| Client | Support |
|---|---|
| Outlook 365 | Works |
| Outlook (New) | Works |
| Outlook iOS | Works |
| Outlook Android | Works |
| Outlook for Mac | Works |
| Apple Mail | Works |
| Apple Mail iOS | Works |
| Yahoo Mail | Works |
| Yahoo Mail Android | Works |
| Yahoo Mail iOS | Works |
| Samsung Mail | Works |
| Thunderbird | Works |
| Proton Mail | Works |
| AOL Mail | Works |
| Fastmail | Works |
Caveats (1)
- 1. Gmail Android: Partial. Supported with non Google accounts only.
Caveats as recorded by caniemail (MIT), one entry per wording.
How <rt> behaves
The <rt> element marks the pronunciation annotation in ruby text. Email client support is uneven, some clients render <rt> above the base text correctly, while others render it inline as adjacent characters, which can corrupt the visual reading order.
- Apple Mail and modern Gmail render ruby correctly with <rt> stacked above the base.
- Outlook Classic often inlines <rt> content, breaking the visual hierarchy.
- Mobile webmail clients are inconsistent, test extensively before relying on ruby in production.
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