MIME parsing is the process of reading and interpreting the structured parts of an email message, including headers, body sections, attachments, encodings, and nested multipart content. Mail clients use MIME to turn raw message data into something a user can view safely and correctly.
This matters because email is untrusted input. Attackers can craft messages with unusual boundaries, malformed headers, nested parts, or tricky encodings to confuse parsers and trigger bugs in rendering or attachment handling. Those bugs may lead to crashes, content spoofing, phishing bypasses, or even code execution in severe cases. Defenders reduce risk by keeping mail clients patched, limiting active content, validating attachments, and treating complex MIME handling as part of the endpoint attack surface rather than a simple display function.