Supported Formats
MailMode focuses on practical email source formats used by email developers and marketing teams.
HTML and HTM Emails
Standard HTML/HTM email files are the simplest path. MailMode sanitizes or restricts scripts where needed, renders the markup in controlled preview frames where possible 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 is intended for static templates, simple props and standard React Email components. Dynamic logic, hooks, browser APIs, external data and complex runtime rendering should be rendered to HTML before previewing in MailMode.
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 for previewing. If you create a hosted share link, see Shareable Previews for how temporary hosted previews work.
Current Limitations
MailMode is intended for practical previewing and QA, not as a replacement for every project build pipeline. Dynamic React Email features may be blocked for safety, and complex templates should be rendered externally first.
Best Practices
Use inline styles for core layout and colours. Keep dark mode CSS explicit. Add meaningful alt text. Include subject and preheader source where supported. Avoid relying on scripts, and test the rendered output in MailMode plus real clients for final QA. For the fastest path, start with Quick Start.