MIME - Multipurpose Internet Mail Extension

MIME is a standard which was proposed by Bell Communication in 1991 in order to expand the limited capabilities of E-mail. E-mail has simple structure earlier. E-mail was able to send message only in NVT 7-bit Ascii format.

In short, MIME is a supplementary protocol or a add-on which allows non-ascii data to be sent through emails (using smtp).

It allows users to exchange different kind of data files on internet such as audio, video and images. MIME is an extension to Internet protocol. E-mail message with mime formatting are typically transmitted with standard protocol like SMTP, POP, IMAP. Although MIME was designed mainly from SMTP its content type are also important in other communication protocols.

Example -: In HTTP protocol for 'www' server insert a MIME in header field at the beginning of any web transmission.

Why MIME is Used?

SMTP has very simple structure.
SMTP can only send message in NVT 7-bit ascii format.
Earlier E-mail can't be send for languages that doesn't support 7-bit ascii format such as French, German. so in order to make SMTP more broad we use MIME.
It can't be used to send binary files or audio or video files.

MIME Header

It is added to the original e-mail header section to define transformation.

There are 5 headers which we add to original header.

1) MIME version

2) Content Type -(defines type of data used in message)

3) Content Transfer Encoding - Tells method used for encoding (e.g, 8 bit encoding)

4) Content Id - Helps in uniquely identifying the message

5) Content Description - It defines whether the body is actually image, video or audio.

S/MIME in Cryptography

S/MIME stand for secured multipurpose internet mail extension protocol. It provides security to the commercial emails. It is extension to MIME.

It is widely accepted method for sending digitally signed and encrypted messages. S/MIME is based on asymmetric based key encryption. S/MIME allows us to digitally sign our e-mails to verify ourself as a legitimate entity. In simple word S/MIME is used to encrypt e-mails and digitally sign them.