3.L E-mail Basic Concept 3.1.1 E-mail and its code E-mail as one of the most basic functions of Internet, has become an indispensable communication means. In fact, all types of information, including text files, graphics files, sound files, etc., can be transmitted through networks in the form of an E-mail attachment. In addition to the fast information sharing of fast information can be achieved by e-mail, users can perform project management through E-mail, and conduct important decision actions based on fast e-mail information exchange. During the transfer of computer information, in order to ensure that the sender and the receiver can correctly identify the transmitted information, the transmitted information is required to encode the transmitted information, and only the computer information can be Transfer and understand correctly. During the transmission and transmission of E-mail, the information is also required to encode and decode information. Reviewing the development of E-mail, it can be seen that the INTERNET mail protocol initially sent and receiving E-mail, just to transfer English text (ie, the 7-bit ASCII character consisting of text), therefore, the email protocol at that time can only support the sending and receiving ASCII text. . With the continuous development of the Internet, the information on online transmission is increasing, which requires new ways to transmit the original ASCII text, and can transmit binary, including images, sounds, and software. Document, this new approach is to encode and decode. The encoding is converted into a text file format, and the decoding is just the opposite. The encoding in e-mail mainly involves the following three ways: 1. UUEE coding UUENCODE and Uudecode originally used by the encoding and decoding programs used in the UNIX system, later rewritten to become a program that can be executed in DOS. . This is the most common way to transfer non-ASCII code, this UU encoding method is the most commonly used. The UU coding is: Before sending E-mail, use the uuencode.exe program to encode the original file into the ASCII code file, then send the encoded e-mail, and then receive E-mail, Restore the file again with the Uudecode program. WINDOWS-based similar programs are Wincode and Winzip, etc., their working principle and uuencode and uudecode under DOS are nothingord, but it is easier to operate under Windows interface. In addition, Wincode also supports MIME, BIN HEX and other encoding formats, and the application range is quite wide. 2. Multipurpose Internet Mail Extensions UU Coding Although the E-mail can only transmit the ASCII file, this method is not very convenient, so people have developed a new coding standard, MIME standard Multimedia files can be transmitted, and they can be sent together in a variety of formats in E-mail. The advantage of the MIME standard is to package a variety of different files together with an accessory. The sender will select the file to be transmitted, and when the transmission is time to send, the information that the acceptor receives the instant decoding restore, which is fully automated. It is very convenient. Of course, the prerequisite is that the software of both sides must have this function. Otherwise, if the sender is very convenient to send the letter, but if there is no such function, it is not possible to see it. Pile of mess. Using the MIME standard encoding method, the user does not need to know how it is decoded. Even if it is just written by words, it is the same as the package.
