Multipurpose Internet Mail Extensions (MIME) is an Internet standard that extends the format of email to support:
- Text in character sets other than ASCII
- Non-text attachments: audio, video, images, application programs etc.
- Message bodies with multiple parts
- Header information in non-ASCII character sets
Virtually all human-written Internet email and a fairly large proportion of automated email is transmitted via SMTP in MIME format.
MIME is specified in six linked RFC memoranda: RFC 2045, RFC 2046, RFC 2047, RFC 4288, RFC 4289 and RFC 2049; with the integration with SMTP email specified in detail in RFC 1521 and RFC 1522.
Although MIME was designed mainly for SMTP, the content types defined by MIME standards are also of importance in communication protocols outside of email, such as HTTP for the World Wide Web. Servers insert the MIME header at the beginning of any Web transmission. Clients use this content type or media type header to select an appropriate viewer application for the type of data the header indicates. Some of these viewers are built into the Web client or browser (for example, almost all browsers come with GIF and JPEG image viewers as well as the ability to handle HTML files).