What "compatibility" means here
Every component page shows a compatibility matrix with ratings like Full, Partial, or None for each email client. This guide explains where those ratings come from and how to use them.
Analysis vs. live testing
Compatibility data comes from static analysis of the HTML and inline styles against documented behavior of each email client. It does not come from live inbox testing in services like Litmus or Email on Acid.
This matters: we can reliably flag known incompatibilities (Outlook ignoring border-radius, Gmail stripping <style> blocks, Apple Mail inverting colors in dark mode) based on documented client behavior. What we cannot guarantee is how a specific version of Outlook on a specific Windows build will render a particular combination of styles on a given day.
We are honest about this distinction. "Full" means no known incompatibilities from static analysis, not "we tested this in all 800 email client configurations."
The compatibility ratings
| Rating | What it means |
|---|---|
| Full | No known incompatibilities from static analysis. Renders correctly based on documented client behavior. |
| Partial | Known limitations exist but the component degrades gracefully — functionality is preserved, appearance may differ. |
| None | The client does not support a key feature this component relies on, or the component has not been validated for this client. |
Email clients covered
Gmail (Web, iOS, Android)
Gmail strips <style> blocks from the <head> and requires inline styles. All EmailingSimply components use inline styles only.
Gmail on iOS and Android applies dark mode transformations that can invert background colors and text colors. Components rated "Partial" for Gmail dark mode have colors that may invert unexpectedly.
Apple Mail (macOS and iOS)
The most standards-compliant desktop email client. Apple Mail supports many CSS properties that Outlook ignores. It also applies aggressive dark mode color inversion. Components with explicit color-scheme and prefers-color-scheme handling are rated "Full" for dark mode support.
Outlook (Windows)
Outlook on Windows uses the Microsoft Word rendering engine — not a browser. This is the source of most email compatibility challenges:
- No
border-radiussupport on table cells (shows as square corners) - No
background-imageCSS support (requires VML fallback) - No
flexboxorgrid(requires table-based layout — which is what all components use) - Conditional comments (
<!--[if mso]>) are used to target Outlook specifically
Components that use VML for Outlook-compatible background images are rated "Full" for Outlook support. Components that simply degrade to a flat color fallback are rated "Partial."
Outlook.com (web)
The web version of Outlook has better CSS support than the desktop client but still strips some properties. Generally more permissive than desktop Outlook.
Yahoo Mail
Good CSS support. Inline styles work reliably. Some advanced features like CSS animations are not supported, but EmailingSimply components do not use them.
Dark mode support levels
Full dark mode support means the component uses explicit dark mode techniques:
prefers-color-scheme: darkmedia query (for supporting clients)- Explicit
color-schemedeclarations - High-contrast dark colors defined in the HTML
Partial dark mode support means the component has some dark-safe colors but may have unintended inversions in aggressive dark mode clients like Apple Mail iOS.
No dark mode support means the component uses colors that are likely to invert poorly in dark mode. It will still be usable but may look bad in dark mode email clients.
Testing your own emails
For production emails, we strongly recommend testing in a real inbox testing service before sending. Tools like Litmus or Email on Acid render your email in hundreds of real email client configurations.
EmailingSimply's HTML Analyzer can catch common issues before you reach an inbox testing service. The Dark Mode Analyzer specifically flags potential dark mode rendering problems.
Reporting compatibility issues
If you find a compatibility issue that is not reflected in a component's matrix, please get in touch. We update compatibility data as we learn more.