What transport protocols are commonly used for email?

The transmission protocol usually used by email is "SMTP". SMTP means "Simple Mail Transfer Protocol" in Chinese. It 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. 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 operating environment of this tutorial: Windows 7 system, Dell G3 computer.

E-mail protocols include SMTP, POP3, and IMAP4, which all belong to the TCP/IP protocol cluster. By default, connections are established through TCP ports 25, 110, and 143 respectively.

The transmission protocol commonly used for email is SMTP.

SMTP protocol

The full name of SMTP is "Simple Mail Transfer Protocol", which is a simple mail transfer protocol. A protocol for 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 reliable and orderly data flow channel support. 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.

Function:

SMTP is a set of rules for transmitting emails from a source address to a destination address, and controls how letters are transferred. The SMTP protocol belongs to the TCP/IP protocol suite, which helps each computer find the next destination when sending or relaying letters. Through the server specified by the SMTP protocol, we can send the E-mail to the recipient's server. The whole process only takes a few minutes. The SMTP server is a sending email server that follows the SMTP protocol and is used to send or relay emails sent by users.

SMTP is a protocol that provides reliable and efficient email transmission. It 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.

One of the important features of SMTP is its ability to transmit mail across the network, also known as "SMTP mail relay". Using SMTP, mail transmission can be realized between processors on the same network, and mail transmission between a certain processor and other networks can also be realized through a relay or gateway. Mail exchange servers with Domain Name Service (DNS) functionality can also be used to identify the next-hop IP address for transmitting mail.

Working process

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

(1) Establishing a 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.

Extended knowledge:

POP protocol

POP post office protocol is responsible for retrieving from the mail server e-mail. It requires the mail server to complete one of the following tasks: retrieve the mail from the mail server and delete the mail from the server; retrieve the mail from the mail server but not delete it; do not retrieve the mail and just ask if any new mail has arrived. The POP protocol supports the Multi-User Internet Mail Extension, which allows users to attach binary files to emails, such as word processing files and spreadsheet files. This allows virtually any file format to be transferred, including images and sound files. When the user reads the mail, the POP command downloads all the mail information to the user's computer immediately and does not keep it on the server.

POP3 (Post Office Protocol 3) is the third version of the Post Office Protocol and is the first offline protocol standard for Internet email.

IMAP Protocol

Internet Information Access Protocol (IMAP) is a new protocol that is superior to POP. Like POP, IMAP can download mail, delete mail from the server, or ask for new mail, but IMAP overcomes some of POP's shortcomings. For example, it can determine how the client requests the mail server to submit incoming mail, requesting the mail server to download only selected messages rather than all messages. The client can read the title of the email message and the name of the sender before deciding whether to download the email. Through the user's client email program, IMAP allows users to create and manage mail folders or mailboxes on the server, delete mail, and query part or all of a letter, all without removing the mail from the server. Downloaded to the user's personal computer.

Commonly used email clients that support IMAP include: ThunderMail, Foxmail, Microsoft Outlook, etc.

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