What is This Database?
Email clients vary wildly in how they render HTML and CSS. This database documents known quirks, rendering issues, and workarounds for the clients we've covered so far. Whether you're building HTML emails or debugging a rendering problem, you'll find practical solutions here. We're actively adding more clients — check back as coverage grows.
Browse by Email Client
More clients coming soonAOL
2 quirksAOL Mail uses a web-based interface similar to Yahoo (both on Oath platform historically). CSS support is moderate.
View quirks →Apple Mail
3 quirksApple Mail on macOS and iOS has good CSS support, but has some quirks unique to WebKit.
View quirks →Gmail
3 quirksGmail is one of the most modern email clients with strong CSS support. However, it has some unique quirks.
View quirks →Outlook
4 quirksOutlook (especially on Windows) is notorious for poor HTML email support due to its Word rendering engine. This creates many unique challenges.
View quirks →ProtonMail
2 quirksProtonMail is a privacy-focused email client with restricted CSS support for security reasons.
View quirks →Thunderbird
2 quirksThunderbird is an open-source email client with Gecko engine (like Firefox). CSS support is good but has some quirks.
View quirks →Yahoo Mail
2 quirksYahoo Mail is a web-based client with decent modern CSS support, but has some quirks around media queries and CSS specificity.
View quirks →Quick Tips
- Always test your emails: Use tools like MailViewr to preview how your email renders across clients
- Use inline styles: Many email clients strip class-based styles, so use inline styles when possible
- Provide fallbacks: Not all clients support the same CSS features. Always have a plan B
- Test with real clients: Email testing services provide accurate rendering previews
- Stay informed: Email client support changes over time. Check compatibility matrices regularly
Most Common Quirks
- Outlook (Windows): Uses Word rendering engine, severely limiting CSS support
- Gmail: Strips unused CSS and filters out style tags in certain scenarios
- Apple Mail: Auto-detects phone numbers and dates, modifying styling
- Yahoo & AOL: Aggressively reset styles and strip certain CSS properties
- ProtonMail: Strips almost all CSS for privacy and security
Related Resources
- CSS Support Matrix — See which CSS properties work in which clients
- Email Client Support Matrix — Compare features across clients
- Blog Articles — In-depth guides on email development best practices