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What is SMTP ?

 SMTP 
-SMTP stands for simple mail transfer   protocol.
-SMTP is an application layer protocol.
-The transfer protocol of SMTP is TCP(Transmission control protocol)    because TCP is a reliable and connection Oriented protocol.TCP gurantees e-mail delivery .
-It uses TCP port 25.
-A few webmail services like G-mail use   unofficial port 465 for SMTP.
-SMTP requires each message in 7-bit   ASCII(American Standard Code for   Information Interchange ) format.


-SMTP is used by the client to send mail to servers because SMTP is a push protocol.It is used to send mail from sender to senders mail server and it is also used to send mail to receivers mail server from senders mail server .
- Recepient download the mail from the mail server using POP3 or, IMAP .They can also just view the mail on the server by using webmail.
Some SMTP commands: 
•HELO and EHLO:-Command that initiate a new protocol session  between client and Server.The EHLO command request them to respond with any optional SMTP extension it support.
•MAIL FROM:- Identify sender.
•RCPT To:- To identify intended recipient .
•DATA:-send actual data.
•QUIT:-Terminates the conversation with   the server.


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