What protocol is used to deliver email to mail servers on the Internet?

The SMTP protocol is used to deliver email to mail servers on the Internet. SMTP is a protocol that provides reliable and efficient email transmission. It is mainly used to transfer email information between systems and provide notifications about incoming letters.

The SMTP protocol is used to deliver email to mail servers on the Internet.

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 a relatively simple text-based protocol. One or more recipients of a message are specified (in most cases confirmed to exist) and the message text is transmitted. You can easily test an SMTP server using the telnet program. SMTP uses TCP port 25. To determine an SMTP server for a given domain name, MX (Mail eXchange) DNS is used.

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 the same network processing processes, and mail transmission between a certain processing process and other networks can also be realized through a relay or gateway.

Working process

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

(1) Establish connection: At this stage, The SMTP client requests to establish a TCP connection with the server's port 25. 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.

The above is the detailed content of What protocol is used to deliver email to mail servers on the Internet?. For more information, please follow other related articles on the PHP Chinese website!