Definition
Client support describes the varying levels of HTML and CSS feature support across different email clients (Gmail, Outlook, Apple Mail, Yahoo, etc.). Unlike web browsers, which largely follow web standards, email clients each apply their own rendering engine and CSS transformations, creating significant inconsistencies in how emails display.
Understanding client support is essential for email designers to create emails that work reliably across the diverse ecosystem of email clients their subscribers use.
Client Support Tiers
| Tier | Description | Examples |
|---|---|---|
| Full | Broad CSS support, modern standards | Apple Mail, Outlook for iOS/Android |
| Moderate | Good support with known gaps | Outlook.com, Yahoo Mail, Samsung Mail |
| Limited | Restricted CSS, basic rendering | Gmail (significant CSS stripping) |
| Legacy | Outlook-specific rendering engine | Outlook for Windows (Word rendering) |
Key Feature Support
| Feature | Apple Mail | Gmail | Outlook.com | Outlook (Win) | Yahoo |
|---|---|---|---|---|---|
| Media queries | Yes | Yes | Yes | No | Yes |
| Web fonts | Yes | No | Limited | No | Limited |
| CSS animations | Yes | No | Some | No | No |
| Background images | Yes | No | Yes | No | Limited |
| Border-radius | Yes | Yes | Yes | No | Yes |
| Flexbox | Yes | Partial | Partial | No | Partial |
| CSS Grid | Yes | No | No | No | No |
| AMP for Email | No | Yes | No | No | No |
Testing for Client Support
- Use email testing tools: Litmus and Email on Acid provide rendering previews across 100+ clients
- Build progressively: Design for the lowest common denominator, then enhance for better-supported clients
- Check analytics: Test against the email clients your specific audience uses most
- Maintain a support matrix: Document which features work in which clients for your reference
- Use fallbacks: Always provide fallback styling for unsupported properties
Related Glossary Terms
Dark Mode
Dark mode in email refers to how email clients render messages when the recipient has dark mode enabled. It affects colour display, image rendering, and readability. Designers use CSS media queries and hybrid coding techniques to control the dark mode appearance.
Drag-and-Drop Email Editor
A drag-and-drop email editor is a visual interface that allows marketers to build email layouts by dragging content blocks into place without writing HTML or CSS code.
Email Accessibility Guidelines
Email accessibility guidelines ensure emails are usable by people with disabilities, following WCAG standards for screen readers, colour contrast, keyboard navigation, and readable content.
Email Accessibility
Email accessibility ensures marketing emails are usable by people with disabilities, including those using screen readers, keyboard navigation, or assistive technologies. It follows WCAG 2.1 guidelines for structure, contrast, semantics, and descriptive content.
Email Body
The email body is the main content area of an email message, containing the visible text, images, and structural elements that communicate the message to the recipient.
Email Brand Guidelines
Email brand guidelines document the specific rules for logo usage, colour palette, typography, tone of voice, and component specifications across all email communications.
Frequently Asked Questions
Apple Mail offers the broadest CSS support, following web standards most closely. Outlook for iOS/Android also provides excellent support. Gmail has the most significant CSS limitations, stripping many properties during rendering.
Outlook for Windows uses Microsoft Word's rendering engine, which severely limits CSS support. Use table-based layouts, inline styles, avoid background images, and provide VML fallbacks for advanced visual elements. Test every template specifically in Outlook for Windows.
Email client support changes infrequently but does evolve. Google, Microsoft, and Apple periodically update their rendering engines. Subscribe to email design newsletters and testing tool changelogs to stay informed about support changes.