MIME (Multipurpose Internet Mail Extensions)
Set of standards (RFCs 2045-2049, 1996) that extends the plain-ASCII {{RFC 822}} mail format to carry binary attachments, non-ASCII character sets, and multipart messages by adding Content-Type, Content-Transfer-Encoding, and MIME-Version headers.
MIME, Multipurpose Internet Mail Extensions, is the standard that lets Internet mail carry anything other than 7-bit US-ASCII text. It was first published as the experimental RFC 1341 in June 1992 by Nathaniel Borenstein (then at Bellcore, after his Carnegie Mellon Andrew Mail System work) and Ned Freed of Innosoft. The standards-track version arrived in November 1996 as a five-part series: RFC 2045 (message body format), RFC 2046 (media types), RFC 2047 (encoded-word syntax for non-ASCII headers), RFC 2048 (registration procedures), and RFC 2049 (conformance criteria). MIME does not change the RFC 822 header/body grammar. Instead it adds new headers on top. MIME-Version declares the message follows the standard. Content-Type labels the body with a registered media type such as text/plain, image/jpeg, or multipart/mixed; the multipart types let one message contain many independently labeled parts, which is how attachments work. Content-Transfer-Encoding names the encoding used to fit potentially 8-bit data into a 7-bit transport: the two encodings MIME defines are Base64 (dense, for binary) and Quoted-Printable (readable, for mostly-ASCII text). The original motivation was international character sets rather than attachments. By labeling content explicitly, MIME also made it possible to add new media types over time without changing the mail protocols, and the same Content-Type vocabulary was later reused by HTTP for the web. Media-type registration is now managed by IANA.