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DEFINITION OF SMTP

SMTP is the acronym that corresponds to the expression of the English language Simple Mail Transfer Protocol. In our language, this concept can be translated as Protocol for Simple Mail Transfer.


SMTP is a network protocol that is used to send and receive emails. It should be noted that a network protocol is a set of regulations and rules that allow the circulation of information in a computer network. In this case, SMTP is part of the so-called Internet protocols.

SMTP operation occurs in the context of email services. Due to certain technical restrictions for receiving emails, it is common for SMTP to be used only for sending messages and for receiving it, other Internet protocols are used, such as IMAP (Internet Message Access Protocol) or POP (Post Office Protocol) ).



In the case of SMTP, its function is to allow a client to communicate with a server, enabling the client to send an email to one or more recipients. SMTP works with lines of text to provide the necessary instructions.

There are three commands that makeup SMTP: MAIL, which sets the sender address for parting messages; RCPT, which establishes the recipient of the message (if there are several, it is issued once for each one); DATA, command that sends the content of the message.

When a person sends an email through this protocol, what happens is that the email client (such as Outlook Express or Mozilla Thunderbird) presents the message in question to a mail server through SMTP. The server sends the message to the Mail Transfer Agent (MTA), which appeals to the Domain Name System (DNS) to find the MX record. When it accepts the mail, it, in turn, refers it to a Mail Delivery Agent (MDA), which can revert to SMTP to deliver it to the mail server. Finally, through IMAP, the receiving user can retrieve the message in his email client.

Although the Internet did not become massive until the late 1990s, virtual exchanges began several years earlier. With respect to electronic mail, the first exchange system appeared in 1982, which existed on the network called ARPANET, used by the United States Department of Defense so that state and academic institutions could communicate with each other. This system is defined in RFC 821 and 822 (the acronym for Request for comments, some publications in which the descriptions of various procedures and protocols related to computer networks appear, among which the Internet stands out).

The SMTP defined in the first version of the email was based on the client-server model, which states that the client sends a message to one or more recipients. The content of this communication consists only of lines of text, formed by ASCII characters, with a maximum length of one thousand characters each. It should be noted that the acronym ASCII comes from the American Standard Code for Information Interchange, which translates to the American Standard Code for Information Exchange, and is a series of characters from the Latin alphabet; its most common pronunciation, although it is not easy to deduce, is [asqui].

The server sends responses whose content is nothing more than a code made up of three numbers and then an explanatory text: the first component is used for the response by automaton; the text, on the other hand, is directed to a user, so that he is able to understand the answer. Each replica, data or order belonging to the SMTP protocol is made up of lines of text that are delimited with the character <CRLF>.

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