Mail SMTP ports and their meaning

Today we will talk about what SMTP ports are used for. This is a widely used network protocol for sending mail through TCP / IP networks.

Value

The SMTP mail port was first described in 1982. Often, mentioning the name of the protocol, implies its expansion. This solution is designed to send outgoing mail using the TCP port 25. User-level mail applications usually use SMTP to send messages to the server for further retransmission.

History

SMTP ports originate from two implementations - SNDMSG and Mail Box Protocol. This decision was invented by Ray Tomlinson. The development of technology continued throughout the 1970s, until the Internet appeared in its modern form in the 1980s. It has been proven that SMTP ports work fine if the sending and receiving devices on the network are permanently connected. A special mention deserves the Sendmail solution. This is one of the first messaging agents that used SMTP technology.

Mail Processing

The SMTP port uses domain names to detect records from the recipient's mail exchanger. This is the part of the address on the right side of the @ symbol. Note that the SMTP SSL port is designed for mail sessions using the appropriate protocol and an encrypted connection. After the message is delivered to the local server, the message is retrieved by client applications using the IMAP protocol. It provides access to information and manages mail. Also for the described purposes can be used the POP protocol or proprietary systems like Microsoft Outlook or Lotus Notes. Note that SMTP determines the actual transmission of the message, but not the content. Thus, the wrapper of the message is set, as well as its parameters. However, the title and body of the message do not apply to this process.

Protocol Overview

Through the SMTP port, the sender and recipient of the message communicate with each other. The necessary data is obtained by means of a reliable channel. They are usually a TCP connection. The SMTP session contains the commands sent by the client, as well as the corresponding server responses. As a result, parameters are exchanged. The SMTP operation contains three command / response sequences. MAIL FROM specifies the return address required for the returned messages. RCPT TO names the recipient of the message. This command can be used several times. Once for each recipient.

The DATA command is used directly to send the message text. Speech in this case is about the content of the message, and not about part of its shell. This element consists of the body and the message header, which are separated by an empty string. DATA is essentially a group of commands. However, the server responds to them twice. First of all, directly on the DATA command, thereby notifying the system of its willingness to receive messages. In addition, the response arrives at the end of the data sequence. This is necessary to reject or accept the entire letter. Each of the multiple server responses is positive or negative, as evidenced by its code. The latter can be temporary or permanent. By means of a special code, the server reports that there is a wait for the receipt of additional data from the client. Fully functional servers support the queue of messages for resending in case of errors.

SMTP is the delivery protocol. This solution can not take on demand messages from a specific remote server. To extract mail and manage the mailbox, other protocols are created, including POP, as well as IMAP. The latest technologies should be consulted if the computer is not permanently on or has temporary access to the Internet.

Now let's talk about running a remote queue of emails. This is a feature of SMTP. It allows the remote host to start processing the message queue using the server. Thus, the latter can receive the necessary letters to him using the TURN command. A special ODMR technology allows the relay to relay the message to an authenticated user. E-mail requires the use of only Latin characters when creating an account. For users who do not have access to the English keyboard, the RFC 6531 standard was developed. Thanks to it, the mail has learned to recognize "additional" characters. So we briefly described what SMTP ports are and why they are used.