Multipurpose Internet Mail Extensions (MIME)

Multipurpose Internet Mail Extensions (MIME) is an Internet standard that helps extend the limited capabilities of email by allowing insertion of images, sounds and text in a message. It was proposed by Bell Communications in 1991, and the specification was originally defined in June 1992 for RFCs 1341 and 1342.

MIME was designed to extend the format of email to support non-ASCII characters, attachments other than text format, and message bodies which contain multiple parts. MIME describes the message content type and the type of encoding used with the help of headers. All manually composed and automated emails are transmitted through SMTP in MIME format. The association of Internet email with SMTP and MIME standards is such that the emails are sometimes referred to as SMTP/MIME email. The MIME standard defines the content types which are of prime importance in communication protocols like HTTP for the World Wide Web. The data are transmitted in the form of email messages through HTTP even though the data are not an email.

The features offered by MIME to email services are as follows:

• Support for multiple attachments in a single message
• Support for non-ASCII characters
• Support for layouts, fonts and colors which are categorized as rich text.
• Support for attachments which may contain executables, audio, images and video files, etc.
• Support for unlimited message length.

MIME is extensible because it defines a method to register new content types and other MIME attribute values. The format of a message body is described by MIME using special header directives. This is done so that the email can be represented correctly by the client.

• MIME Version: The presence of MIME Version generally indicates whether the message is MIME formatted. The value of the header is 1.0 and it is shown as MIME-Version: 1.0. The idea behind this was to create more advanced versions of MIME like 2.0 and so on.
• Content-Type: This describes the data’s Internet media type and the subtype. It may consist of a ‘charset’ parameter separated by a semicolon specifying the character set to be used. For example: Content-Type: Text/Plain.
• Content-Transfer-Encoding: It specifies the encoding used in the message body.
• Content-Description: Provides additional information about the content of the message.
• Content-Disposition: Defines the name of the file and the attachment settings and uses the attribute 'filename'.