Is email the most widely used service on the internet?

Yes, email is the most widely used service on the Internet, and the commonly used transmission protocol is "SMTP". The SMTP protocol belongs to the TCP/IP protocol suite, which helps each computer find the next destination when sending or relaying letters.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

E-mail is the most widely used service on the Internet, and the commonly used transmission protocol is "SMTP".

SMTP is a protocol that provides reliable and efficient email transmission. SMTP is an email service built on the FTP file transfer service. It is mainly used to transfer email information between systems and provide notifications about incoming letters. SMTP is independent of a specific transmission subsystem and only requires the support of a reliable and orderly data flow channel. One of the important features of SMTP is its ability to transmit emails across the network, that is, "SMTP mail relay". Using SMTP, mail transmission can be realized between processing processes on the same network, and mail transmission between a processing process and other networks can also be realized through a relay or gateway.

The working process of the SMTP protocol can be divided into the following three processes:

(1) Establish a connection: At this stage, the SMTP client requests port 25 of the server Establish a TCP connection. Once the connection is established, the SMTP server and client begin to advertise their domain names to each other and confirm each other's domain names.

(2) Mail transmission: Using commands, the SMTP client passes the source address, destination address and specific content of the mail to the SMTP server, and the SMTP server responds accordingly and receives the mail.

(3) Connection release: The SMTP client issues an exit command, the server responds after processing the command, and then closes the TCP connection.

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