E-mail (e-mail for short, logo: @, also known as "Yi Meier"), also known as e-mail and e-mail, is a communication method that provides information exchange through e-mail. It is the most widely used service on the Internet: through the e-mail system of the network, users can get in touch with network users in any corner of the world in a very fast way (it can be sent to any destination you specify in the world in a few seconds), and the price is very low (no matter where it is sent, only the telephone and network fees need to be paid). These emails can be in many forms, such as text, images and sounds. At the same time, users can get a lot of free news and special emails to realize easy information search. This is unmatched by any traditional way. E-mail is widely used because of its simple use, rapid delivery, low cost, easy preservation and unimpeded global access, which has greatly changed people's communication methods. In addition, email can be sent in a one-to-many way, and the same email can be sent to many people at the same time. Most importantly, e-mail is a system that directly faces the information exchange between people in the whole Internet and all other network systems. Its data sender and receiver are both human beings, so it greatly meets the communication needs of a large number of people. E-mail refers to the communication mode of transmitting letters, documents, materials and other information by electronic means. E-mail combines the characteristics of telephone communication and postal letters. It can transmit information as quickly as a telephone and make the receiver receive a written record like a letter at the receiving end. E-mail system is also called computer-based mail information system. It undertakes the whole processing process from the mail entering the system to the mail reaching the destination. E-mail can be transmitted not only through telephone network, but also through any communication network. When using the telephone network, you can also use it to transmit information during off-peak hours, which is of special value to commercial mail. An electronic system controlled by a central computer and a small computer for limited users can be regarded as a computer conference system. The working process of editing this email follows the client-server model. Every e-mail is sent with the sender and the recipient involved. The sender constitutes the client and the receiver constitutes the server, which contains many users' e-mails. The sender sends the edited e-mail to the post office server (SMTP server) through the mail client program. The post office server recognizes the address of the recipient and sends the mail to the mail server (POP3 server) that manages the address. The mail server stores the message in the recipient's e-mail box and notifies the recipient that a new mail has arrived. After the recipient connects to the server through the mail client program, he will see the notice sent by the server, and then open his e-mail box to check the mail. Usually, individual users on the Internet can't directly receive e-mail, but apply for an e-mail address of an ISP host, and the ISP host is responsible for receiving e-mail. Once the user's e-mail arrives, the ISP host will move the e-mail to the user's e-mail box and notify the user of the new e-mail. Therefore, when sending an email to another customer, the email is first sent from the user's computer to the ISP host, then to the Internet, then to the recipient's ISP host, and finally to the recipient's personal computer. The ISP host plays the role of "post office" and manages the e-mail boxes of many users. The e-mail address of each user is actually the account name applied by the user. Each user's e-mail account takes up a certain amount of hard disk space of ISP host. Because this space is limited, users should regularly check and read the emails in their email boxes to make room for receiving new emails. Edit the format of the email address in this paragraph on the Internet. The email address is just like your own identity. Generally speaking, the format of e-mail address is as follows: Chinese cannot be used in 123@yojian.com or abc@yoxiang.com. Here, domain_name is the identifier of the domain name, that is, the domain name of the email destination to which the mail must be delivered. Someone is an email address on the domain name. Suffixes generally represent the nature of domain names and area codes. For example: com, edu.cn, gov, org and so on. Domain names are technically mail exchanges, not machine names. Common e-mail protocols are as follows: SMTP (Simple Mail Transfer Protocol), POP3 (post office protocol) and IMAP (Internet Mail Access Protocol). These protocols are defined by the TCP/IP protocol family. SMTP (Simple Mail Transfer Protocol): SMTP is mainly responsible for how the underlying mail system transmits mail from one machine to another. POP (post office protocol): The current version is POP3, which is a protocol for transmitting mail from an e-mail box to a local computer. IMAP (Internet Mail Access Protocol): The current version is IMAP4, which is an alternative protocol to POP3. It provides new mail retrieval and mail processing functions, so that users can see the title summary of the mail without downloading the mail body, and can operate the mail and folder directories on the server from the mail client software. IMAP protocol enhances the flexibility of e-mail, reduces the direct harm of spam to the local system, and relatively saves the time for users to check e-mail. In addition, IMAP protocol can remember users' offline mail operations (such as moving mail, deleting mail, etc.). ) will be automatically executed the next time you open the network connection. At present, two mail acceptance protocols and one mail sending protocol support secure server connection. Support for SSL connections is integrated in most popular e-mail client programs. In addition, many encryption technologies are also applied to the sending, receiving and reading of e-mail. They can provide encryption strength from 128 bits to 2048 bits. One-way encryption and symmetric key encryption are also widely supported.