Overview
ProtonMail is a privacy-focused email client with restricted CSS support for security reasons.
Documented Quirks
1
ProtonMail Strips Most CSS
All versions
Issue
ProtonMail aggressively strips CSS to prevent tracking and protect user privacy. Only basic styles work.
Workaround
Design emails with minimal CSS. Use simple tables and inline styles only. Avoid JavaScript and tracking pixels.
2
ProtonMail Blocks External Content
All versions
Issue
ProtonMail blocks external images and resources by default.
Workaround
Use base64-encoded images or ask users to enable external content.
Related Resources
- All Email Client Quirks — Browse quirks for other email clients
- CSS Support Matrix — See detailed CSS property compatibility
- Email Client Support Matrix — Compare feature support across clients
- ProtonMail CSS Support — Full CSS property breakdown for ProtonMail