HTML email is an email format that uses Hypertext Markup Language to control layout, fonts, colors, images, links, and other visual elements. Unlike plain text mail, it is rendered by the email client, which means the final appearance can differ from the raw message structure that a security gateway inspects.
This matters in cyber security because the rendering layer can be abused to hide phishing cues or create deceptive content that only becomes obvious after display. Attackers use HTML email to build convincing login pages, fake buttons, and even QR-like lures made from tables or text. Defenders may need to analyze rendered content, not just attachments, image files, or OCR output, and apply filtering, link rewriting, and content sanitization to reduce risk.