Today we’ll talk about what SMTP ports are used for. This is a widely used network protocol designed to transfer mail through TCP / IP networks.
Value
The SMTP mail port was first described back in 1982. Often, mentioning the name of the protocol implies its extension. This solution is designed to send outgoing mail using
TCP port 25. Mail-based applications operating at the user level usually use SMTP to send messages to the server for further relaying.
History
SMTP ports come from two implementations - SNDMSG and Mail Box Protocol. This solution was invented by Ray Tomlinson. The development of technology continued throughout the 1970s, until the Internet in its modern form appeared in the 1980s. It has been proven that SMTP ports work fine if the sending and receiving devices on the network are constantly connected. Of particular note is the Sendmail solution. This is one of the first messaging agents to use SMTP technology.
Mail processing
The SMTP port uses domain names to discover records from the recipient's domain mail exchanger. This is the part of the address on the right side of the @ sign. Note that the SMTP SSL port is designed for mail sessions using the appropriate protocol and encrypted connection. After the message is delivered to the
local server, the message is retrieved by the client applications using the IMAP protocol. It opens access to information and manages mail. Also, for the described purposes, the POP protocol or proprietary systems such as Microsoft Outlook or Lotus Notes can be used. Note that SMTP defines the transmission of a message directly, but not the content. Thus, the envelope of the message is set, as well as its parameters. However, the title and body of the message are not relevant to this process.
Protocol Overview
Through the SMTP port, the sender and receiver of the message communicate with each other. The necessary data is supplied through a reliable channel. It is usually a TCP connection. The SMTP session contains the commands sent by the client, as well as the corresponding server responses. As a result, the parameters are exchanged. An SMTP operation contains three command / response sequences. MAIL FROM indicates the return address required for returned messages. RCPT TO calls the message recipient. This command can be used several times. Once for each recipient.
The DATA command is used directly to send message text. In this case, it is about the content of the message, and not about part of its shell. This element consists of a body and a message header, which are separated by an empty line. DATA is essentially a group of commands. However, the server responds to them twice. First of all, directly to the DATA command, thereby notifying the system of its willingness to receive messages. In addition, a response arrives at the end of the data sequence. This is necessary to reject or accept the entire letter. Each of the many 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 additional data from the client. Fully functional servers support a message queue for resending in case of errors.
SMTP is a delivery protocol. This solution cannot take on demand messages from a specific remote server. To retrieve mail and manage the mailbox, other protocols have been created, including POP and IMAP. The latest technology should be consulted if the computer is not always turned on or has temporary access to the Internet.
Now let's talk about starting a remote message queue. This is about the features of SMTP. It allows the remote host to start processing the message queue using the server. Thus, the latter can receive the letters he needs with the help of the TURN command. Special ODMR technology allows relay messages to authenticated users. E-mail requires 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 learned to recognize "additional" characters. So we briefly talked about what SMTP ports are and what they are used for.