HTML email
An email message whose body is formatted with HTML and CSS, allowing rich typography, layout, colors, and images. Most modern email is HTML, but privacy and security considerations require careful rendering.
HTML email uses a Content-Type of text/html and applies HTML markup and inline CSS to produce formatted messages with headings, bold text, colored backgrounds, images, and links. Because email clients render HTML in highly varied environments — from mobile apps to desktop clients to web browsers — HTML email is typically written with inline styles and simplified markup to maximize compatibility.
HTML email introduces privacy and security concerns that plain-text email does not. Remote images (fetched over HTTP when the message is opened) can act as tracking pixels, revealing when you read a message and your approximate location. Malicious messages can attempt to inject scripts or misleading links. Email clients typically block remote images by default and sanitize HTML to remove scripts and dangerous tags.
Mbox Viewer renders HTML email in a sandboxed view that blocks all external network requests, preventing tracking pixels and protecting privacy. The HTML is sanitized before rendering to remove potentially harmful elements. Inline images stored as MIME parts (cid: references) are displayed normally, since they require no network access.
Related terms
An image embedded directly into an HTML email body using a Content-ID (cid:) reference, rather than attached as a separate downloadable file. The image data is stored as a MIME part within the same message.
Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email.