The transmission of email is done through the system software of the Email Simple Transfer Protocol (SimpleMailTransferProtocol, referred to as SMTP), which is an email communication protocol under the Internet. The transmission process of email:

1. The email system is a new type of information system, which is the product of the combination of communication technology and computer technology. The transmission of email is completed through the system software of the Email Simple Transfer Protocol (SimpleMailTransferProtocol, referred to as SMTP), which is an email communication protocol under the Internet.

2. The basic principle of e-mail is to set up an “e-mail system” on the communication network, which is actually a computer system. The hardware of the system is a high-performance, large-capacity computer. The hard disk is used as the storage medium of the mailbox, and a certain storage space is allocated for the user on the hard disk as the user’s “mailbox”. Each user has his own e-mail box. And determine the user name and password that the user can modify at will. The storage space includes three parts of space for storing received letters, editing letters and archiving letters. Users use passwords to open their mailboxes and perform various operations such as sending letters, reading letters, editing, forwarding, and archiving. System functions are mainly implemented by software.

3. The communication of e-mail is carried out between mailboxes. The user first opens his own mailbox, and then sends the mail that needs to be sent to the other party’s mailbox by typing a command. The mail is transmitted and exchanged between mailboxes, and it can also be transmitted and exchanged with another mail system. When the recipient picks up the letter, he uses a specific account to extract it from the mailbox. The working process of e-mail follows the client-server model. The sending of each e-mail involves the sender and the recipient. The sender constitutes the client side, and the receiver constitutes the server. The server contains the e-mail of many users. 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 a message to the mail server (POP3 server) that manages the address. The mail server stores the message in the recipient’s e-mail box and informs the recipient of the arrival of new mail. After the recipient connects to the server through the mail client program, he will see the notification from the server and then open his e-mail box to check the mail. Usually individual users on the Internet cannot receive e-mail directly, but by applying for an e-mail box from the ISP host, the ISP host is responsible for receiving e-mail. Once a user’s e-mail arrives, the ISP host moves the mail to the user’s e-mail box and notifies the user of new mail. Therefore, when an e-mail is sent to another customer, the e-mail 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 a “post office” and manages the e-mail of many users. Each user’s e-mail is actually the account name applied by the user. Each user’s e-mail mailbox takes up a certain amount of hard disk space on the ISP host. Since this space is limited, users should regularly check and read emails in the e-mail box in order to make room for receiving new emails.