NETWORK ~ SMTP📨
The Simple Mail Transfer Protocol (SMTP) is a standard communication protocol for sending e-mail over corporate networks and the Internet. SMTP was developed in the early 1980s and remains one of the most popular protocols in the world.
Mail software generally uses the SMTP protocol for sending and the POP3 (Post Office Protocol 3) or IMAP (Internet Message Access Protocol) protocol for receiving mail. Until now, there is no alternative to the SMTP protocol.
SMTP uses TCP port number 25 for standard communication.
The SMTP protocol is usually integrated into a mail client and consists of four key components:
- Local user known as the Mail User Agent (MUA)
- Called server (MSA - Mail Submission Agent)
- Mail Transfer Agent (MTA)
- Mail delivery agent (MDA)
SMTP works by initiating a session between the user and the server, while MTA and MDA provide domain lookup and local delivery services.
Some SMTP commands:
- HELO and EHLO: Commands to start a new session between the client and the server.
- MAIL: Command to start sending an email.
- RCPT: Command to provide an email address to the recipient of the message being prepared.
- DATA: Command to indicate the beginning of the message transmission.
- RSET: while sending an email (after issuing the MAIL command), either end of the SMTP connection can reset the connection if it encounters an error.
- NOOP: an empty message ("no operation") designed as a kind of ping to check the responsiveness of the other end of the session.
- QUIT: terminates the protocol session.
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