What is Network Automation?

SMTP Commands

Last Updated : 13 Sep, 2021

Simple Mail Transfer Protocol (SMTP) is an ASCII protocol. It is based on client-server model. It uses TCP port number 25 for this service. Therefore e-mail; is delivered from source to destination by having the source machine established a TCP to port 25 of the destination machine. To send mail, a system must contain client MTA and to receive a mail, a system must have server MTA. SMTP transfers this message from client MTA to the server MTA. To send a mail, SMTP is used two times: one between sender and sender's mail server and the other between the two mail servers.

SMTP Commands :
These commands are sent from the client to the server. Each command consists of a keyword followed by zero or more arguments. It means there are also some keywords that do not contain any argument. The format of the command is as follows :

 Keywords : argument(s)

There are 14 different SMTP commands which are given in the following table :

S.No.	Keyword	Command form	Description	Usage
1.	HELO	HELO<SP><domain><CRLF>	It provides the identification of the sender i.e. the host name.	Mandatory
2.	MAIL	MAIL<SP>FROM : <reverse-path><CRLF>	It specifies the originator of the mail.	Mandatory
3.	RCPT	RCPT<SP>TO : <forward-path><CRLF>	It specifies the recipient of mail.	Mandatory
4.	DATA	DATA<CRLF>	It specifies the beginning of the mail.	Mandatory
5.	QUIT	QUIT<CRLF>	It closes the TCP connection.	Mandatory
6.	RSET	RSET<CRLF>	It aborts the current mail transaction but the TCP connection remains open.	Highly recommended
7.	VRFY	VRFY<SP><string><CRLF>	It is use to confirm or verify the user name.	Highly recommended
8.	NOOP	NOOP<CRLF>	No operation	Highly recommended
9.	TURN	TURN<CRLF>	It reverses the role of sender and receiver.	Seldom used
10.	EXPN	EXPN<SP><string><CRLF>	It specifies the mailing list to be expanded.	Seldom used
11.	HELP	HELP<SP><string><CRLF>	It send some specific documentation to the system.	Seldom used
12.	SEND	SEND<SP>FROM : <reverse-path><CRLF>	It send mail to the terminal.	Seldom used
13.	SOML	SOML<SP>FROM : <reverse-path><CRLF>	It send mail to the terminal if possible; otherwise to mailbox.	Seldom used
14.	SAML	SAML<SP>FROM : <reverse-path><CRLF>	It send mail to the terminal and mailbox.	Seldom used

What is Network Automation?

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