What Is MIME?

Date First Published: 24th March 2022

Topic: Computer Networking

Subtopic: Network Standards

Article Type: Computer Terms & Definitions

Difficulty: Medium

Difficulty Level: 6/10

CONTENTS

RFC Requests
MIME Types
History

Learn more about what MIME is in this article.

Short for Multipurpose Internet Mail Extensions, MIME extends the original SMTP and enables users to use text in character sets other than ASCII, layouts, fonts, and colours that are categorised as rich text. It also supports unlimited message length, attachments of images, audio, videos, documents, and more in an email message. It is a method of transferring non-text files through email messages. MIME consists of two parts, called a type and a subtype. For example, the MIME type of a plain text file is text/plain.

The creation of MIME was mostly designed for SMTP. However, its content types are used in other protocols, such as HTTP. In HTTP, which is used by the World Wide Web, a MIME header field is inserted at the beginning of a web transmission by servers, which looks like: content-type: text/html. This is used for identifying the type of data that is accessible from a URL.

Note:

MIME is extensible because it has the capability to be extended or customised from its original state in order to make it appropriate for the tasks that need to be performed with it. For example, MIME specifies a method to register new content types and other MIME attribute values.

RFC Requests

MIME is defined in a number of requests in RFC 2045, RFC 2046, RFC 2047, RFC 4288, RFC 4289, and RFC 2049. In RFC 1521 and RFC 1522, the combination with SMTP is defined.

MIME Types

MIME types are assigned by IANA. Several different MIME types exist, such as:

Text/html - HTML file (webpage)
Text/css - CSS file (webpage stylesheet)
Text/javascript - JavaScript file
image/jpeg - JPEG file (image)
image/png - PNG file (image)
audio/wav - WAVE audio file (audio)
video/mp4 - MPEG audio file (video)
application/zip - ZIP file (compressed folder)

History

MIME was proposed by Bell Communications in 1991 and defined in June 1992 in RFC 1341 and RFC 1342. MIME was created as a cross-platform alternative to the Andrew-specific data format by the Andrew Messaging System, which was part of the Andrew Project developed at Carnegie Mellon University (CMU).

SMTP was originally capable of supporting the sending of emails, but not file transfers. This meant that it was necessary for email attachments to be converted as part of the message and resulted in limitations in terms of size. The introduction of MIME made it easier for files to be sent through email using a custom content-type header. SMTP still makes use of this method. Email messages containing attachments include a header, which looks like: content-type: multipart/mixed; boundary =”[identifier]”.