Email client support
MailInApp's fallback engine targets the real rendering capabilities of today's email clients — verified against caniemail.com and hands-on client testing, and re-checked as clients evolve. This is the support picture the engine is built around (last verified July 2026).
Capability matrix
| Capability | Gmail | Apple Mail | Outlook classic (Windows) | New Outlook / Outlook.com | Yahoo Mail | Samsung Mail |
| --- | --- | --- | --- | --- | --- | --- |
| Embedded styles & media queries | ✅ * | ✅ | ❌ | ✅ | ✅ | ✅ |
| Kinetic CSS (:checked interactivity) | ✅ | ✅ | ❌ | ⚠️ partial | ✅ | ⚠️ partial |
| In-email form submission | ✅ web/Android | ⚠️ version-dependent | ❌ | ⚠️ unreliable | ✅ | ⚠️ |
| CSS animation | ✅ | ✅ | ❌ | ✅ | ✅ | ✅ |
| AMP for Email | ✅ registration required | ❌ | ❌ | ❌ | ✅ | ❌ |
| Plain links | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
* Gmail strips embedded styles in one edge case: the Gmail mobile app reading a non-Gmail (IMAP) account. Those readers get the static tier.
Plain links are the only capability with truly universal support — which is why every MailInApp interaction has a link-based path.
What each client receives
- Gmail (web, Android, iOS) — kinetic tier: working carousels, accordions, polls. In-email form posts on web and Android; hosted form fallback on iOS.
- Apple Mail (macOS, iOS) — kinetic tier.
- Yahoo Mail — kinetic tier, including in-email form posts.
- Samsung Mail — kinetic tier with conservative enhancements; anything uncertain falls back to static.
- New Outlook & Outlook.com — static tier with selected safe enhancements. Form posts are unreliable there, so forms use the hosted-page path.
- Classic Outlook (Windows) — the dedicated Outlook tier: table-based layout via conditional comments, static content, GIF countdowns (first frame chosen to be meaningful, since very old versions show only the first frame), and live-view links for everything interactive.
About Outlook's transition
Microsoft is migrating classic Outlook users to the Chromium-based New Outlook through 2026–2027. Until that completes, both engines are first-class targets: conditional comments are only honored by the classic Word engine, which makes them a safe way to target it exclusively.
Our testing order
New techniques are validated against clients in order of real-world reach: Gmail web → Gmail mobile → Apple Mail → classic Outlook → New Outlook/Outlook.com → Yahoo → Samsung. A technique that can't pass this gauntlet with a clean fallback story doesn't ship — see How fallbacks work.