Supported Formats
MailMode focuses on practical email source formats used by email developers and marketing teams.
HTML and HTM Emails
Standard HTML email files are the simplest path. MailMode sanitizes scripts, renders the markup in sandboxed previews and analyses the static source for common email risks. Inline styles usually produce the closest result to real inbox rendering.
MJML
MJML files are compiled before previewing. MailMode detects MJML title and preview tags where available, then runs the same preview and health checks on the rendered output. Some advanced MJML setups, includes and custom component workflows may need to be rendered externally first.
React Email
React Email JSX/TSX support uses safe static preview mode. It supports static component trees, standard React Email components, string and number props, and static inline style objects.
ZIP Email Projects
ZIP uploads can contain one main HTML, HTM, MJML, JSX or TSX file plus local images. MailMode validates file types, rejects nested ZIPs and unsafe paths, and processes assets temporarily in browser memory.
Current Limitations
Dynamic React Email features such as .map() loops, runtime conditionals, hooks, effects, browser APIs and dynamic function execution may be blocked for safety. For complex templates, export rendered HTML and paste that into MailMode.
Best Practices
Use inline styles for core layout and colours. Keep dark mode CSS explicit. Add alt text for meaningful images. Include a subject/preheader source where your format supports it. Avoid relying on scripts or external resources for rendering.