MIME

MIME, or Multipurpose Internet Mail Extensions, is a specification that extends the original Internet mail protocol to support non-ASCII characters and a broad range of multimedia content. Defined in RFC 2045 through RFC 2049, MIME introduces mechanisms for classifying, encoding, and transporting content so different systems can interpret it correctly, including email clients, servers, and web browsers. Although created for email, MIME has been adopted by other protocols, notably HTTP, to convey the type and encoding of message bodies.

MIME content types (also called media types) describe the nature of the data. A type consists of a type and a subtype, for example text/plain, image/jpeg, or application/json. Optional parameters follow after a semicolon, with charset for text types being common. The registry of registered types is maintained by IANA. In HTTP, a Content-Type header communicates the media type to clients.

To carry non-text data over text-based channels, MIME defines content-transfer-encodings such as 7bit, 8bit, binary, quoted-printable, and base64. For messages that contain multiple parts, MIME defines multipart types (e.g., multipart/mixed, multipart/related, multipart/alternative) with boundary markers to separate parts within a single message. Text parts may specify a character set and language.

Practical use: email attachments and inline content, REST and web APIs exchanging data in JSON or XML, and web servers delivering multimedia. MIME types are registered and standardized to enable correct handling by software; mislabeling content that does not match its declared type can lead to security issues and improper rendering.