Brief introduction and analysis of MIME Protocol

As we know, today's emails have basically replaced traditional emails. E-mails can be described in texts and loaded with music images and other multimedia forms. As the network continues to innovate, mail can also carry different types of files for transmission. This requires the support of the MIME protocol.

Multi-purpose Internet Mail Extension protocol MIME) is the abbreviation of Multipurpose Internet Mail Extensions. It describes how to arrange message formats for messages to be exchanged in different email systems. The MIME format is flexible, allowing emails to contain any type of files. MIME messages can contain specific data of text, images, sounds, videos, and other applications. Specifically, MIME allows emails to include:

A single message can contain multiple objects;

A text document does not limit the length of a line or full text;

Messages in non-English languages can be transmitted in character sets other than ASCII;

Multi-font messages;

Binary or specific application files;

Images, sounds, videos, and multimedia messages.

The MIME protocol composite message directory header has a boundary mark. This boundary mark must not appear in other positions of the message, but only between departments and the beginning and end of the message body.

MIME Protocol Security version S/MIMESecure/Multipurpose Internet Mail Extensions) is designed to support Mail encryption. Based on the MIME standard, S/MIME provides the following encryption security services for electronic message applications: authentication, integrity protection, authentication, and data confidentiality.

Traditional email user proxy MUA can use S/MIME to encrypt and decrypt and receive emails. However, S/MIME is not limited to the use of mail, it can also be applied to any mechanisms that can transmit MIME data, such as HTTP. Similarly, S/MIME uses MIME's object-oriented features to allow secure message exchange in a hybrid transmission system.

In addition, S/MIME can also be applied to automatic message transfer agents, which use encryption security services that do not require any operation, such as software document signatures and FAX encryption sent to the Internet.

MIME protocol structure

The MIME mail header field is defined as follows:

Object Header: = [directory CRLF] [encoding CRLF] [id crlf] [description CRLF] * MIME extension field CRLF)

MIME message header: = entity Header

Field

CRLF version

Message Header defined in BNF

Segment sequence should be ignored;

MIME local header: = Object Header

[Field]

No field starting from "directory"

It does not have a specific meaning. You can ignore it.

Message Header defined in BNF

Segment sequence should be ignored;

The message format and the S/MIME implementation process can be viewed in related files.