SMTP - Simple Mail Transfer Protocol. Know more about it here.

The word SMPT stands for Simple Mail Transfer Protocol. Emails are sent from one email address to the other based on the SMTP. The main purpose of the SMTP server is to send, receive and relay emails.

How does the SMTP server work?

There are a set of commands through which the servers talk to each other. Given below are the basic commands and their role.

250ok (response code): Whenever a successful communication happens from a sender server, 250ok is the response code the recipient server provides for helo, mail from, and RCPT TO commands.

HELO or EHLO (Hello):?It is basically, the sender server initiating the conversation by saying HELO to the recipient server.

MAIL FROM:?This command specifies the sender domain address to the recipient server and tells that the communication has begun. The recipient server responds 250ok if the initial from the domain looks good.

RCPT TO (Recipient To): This is to specify the email address of the recipient user.

DATA: The transfer of the data between recipient and sender server begins with this command. All of the message contents will be moved to the SMTP server, which will respond with a 345 reply code.?When you send a single dot in a line that specifies the end of the data transfer.

QUIT: It is used to convey that the message is sent and the connection can be stopped now. Here the response code is 221.

RSET (Reset): This resets the connection and clears the previous email details. You can now initiate e new email sending process.

The below image gives a clear picture of the SMTP communication between the two servers.

@ CP: Image Reference from Postmarkup site.

Please let me know of any questions or comments.