Email previews often contain sensitive material. Treat thread specifications and generated HTML as confidential unless the owner explicitly approves publication.

• User-provided text is HTML-escaped.
• Link cards accept only absolute http and https URLs.
• Avatar colors must be six-digit hex values.
• Generated pages contain no remote fonts, scripts, analytics, or image requests.
• Public examples use synthetic people and destinations.

Please open a GitHub security advisory rather than a public issue for a vulnerability that could expose preview content or bypass renderer validation.