How SMTP Works?

Many people today send and receive emails. It is one of the fastest means of exchanging information in vogue today. However, only a few people that use it know how it functions. SMTP which is an acronym for simple mail transfer protocol (SMTP) is the standard for the internet that makes email possible. Here you’ll learn more about Simple Mail Transfer Protocol (SMTP).

What is Simple Mail Transfer Protocol?

Simple Mail Transfer Protocol shortly called SMTP refers to the protocol utilized when electronic mails are being sent from client to the receiver. It makes the transfer of e-mails from clients’ servers to the recipients’ servers and vice versa possible. SMTP which works with TCP well Known port 25 is the application level protocol that deals with message service over TCP/IP networks. It was in 1981 that the protocol was defined in RFC 788 for the first time. But it was revised in RFC 821 and RFC 822 in 1982. The 821 and 822 definitions were also revised and released in 2001 as RFC 2821 (SMTP) and RFC 2822 (internet message format) respectively.

How does SMTP work?

When you buy SMTP, it delivers message from one end to another. When a client click on the “send button” of your email in order to send an email to a person, the server on the internet/network will be connected to by the email program. This server to which the program connects to is what is referred to as the SMTP server. In other words, the client’s SMTP server will contact the recipient’s SMTP server on well-known port 25 in order to send your email. The client will wait for a 220 Ready for Mail message to be sent by the server. The client will send a Helo command when the 220 message is received and a 250 requested mail action okay message will be sent by the server in response.

The email delivery will start with a mail which assigns an identification to the Sender. It will also give a FROM field (the address to which errors are reported is contained in this field). After the MAIL command is successfully executed, a series of RCPT commands will be issued by the sender. The mail message of the recipients will be identified by these series of RCPT commands. Each of these RCPT commands will be acknowledged by sending 250 OK. If there is no user, the error message will be sent.

The sender server will issue a DATA command when all the commands have been acknowledged  to the receiver’s server informing it of the readiness of the sender to deliver a complete mail message. With a message 354 Start mail command, the receiver will respond. It will also provide sender an ending sequence to use in order to end the message data. 5 characters are contained in the termination sequence and they include line feed, carriage return, period, line feed and carriage return (<CRLFY>.<CRLF>).

The data will not be sent by the client server line by line. The receiving server either acknowledges with a 250 and sends an error message when there is something wrong.

At the click of the QUIT command, connection can be closed if there is no more messages to be delivered by the current simple mail transfer protocol client. Through a 221 service closing transmission channel reply answer will be provided.

The entire process is very fast.