Simple Mail Transfer Protocol (SMTP)
Simple Mail Transfer Protocol (SMTP) is a protocol used for sending and receiving emails over the Internet. It is the most widely used protocol for email transmission on the Internet, and is an application layer protocol based on the TCP/IP suite of protocols. SMTP is used to send messages from one computer to another, and it can also be used to send messages from one user to another.
SMTP was first developed in 1982 by Jon Postel, then at the University of Southern California’s Information Sciences Institute. It was designed as a simple way to transfer mail between computers, and has since become the standard for email transmission on the Internet. SMTP is an application layer protocol that uses TCP/IP as its transport layer protocol.
SMTP works by establishing a connection between two computers, usually referred to as a client and a server. The client sends an SMTP command to the server, which then responds with an acknowledgement or error message. The client then sends its message data, which includes information such as sender address, recipient address, subject line, body text, attachments etc., followed by an end-of-data command. The server then processes this data and sends it back to the client with either an acknowledgement or error message.
The main purpose of SMTP is to transfer emails from one computer to another over the Internet. It does this by using a series of commands that are sent between two computers in order to establish a connection and transfer data. These commands are known as Simple Mail Transfer Protocol (SMTP) commands and they are sent using TCP/IP as their transport layer protocol.
The most commonly used SMTP commands are HELO (Hello), MAIL FROM (Sender), RCPT TO (Recipient), DATA (Message Body), QUIT (End Session). Other less commonly used commands include VRFY (Verify Address), EXPN (Expand Address List) and HELP (Help).
When sending emails using SMTP, there are several steps involved:
1) Establishing a connection between two computers using TCP/IP;
2) Sending HELO command from client computer;
3) Sending MAIL FROM command from client computer;
4) Sending RCPT TO command from client computer;
5) Sending DATA command from client computer;
6) Sending message body text;
7) Sending QUIT command from client computer;
8) Receiving acknowledgement or error message from server computer;
9) Closing connection between two computers using TCP/IP.
Once these steps have been completed successfully, the email will be sent successfully over the Internet using SMTP protocol. In addition to sending emails over the Internet, SMTP can also be used for other purposes such as verifying addresses or expanding address lists etc., but these functions are not commonly used today due to security concerns associated with them.
