How SMTP mail server works

Working of SMTP (Simple Mail Transfer Protocol)

SMTP is a simple ASCII protocol that is based on client-server model.

After establishing the TCP connection, the sending machine, operating as the client, waits for the receiving machine, operating as the server, to talk first. The server starts by sending a line of text giving its identity and telling whether or not it is prepare to receive mail. If it is not, the client releases the connection and tries again later.

If the server is willing to accept e-mail, the client announces whom the e-mail is coming from and destination, the server gives the client the go ahead to send the message. Then the client sends the message and the server acknowledges it.

Mail Transfer Phases

The basic SMTP operation occurs in three phases:

1. Mail transfer
2. Connection set up
3. Connection termination

Mail transfer

Once the connection has been established, the SMTP sender may send one or more messages to the SMTP receiver.

There are three logical phases to the transfer of a message:

1. A MAIL command identifies the originator of the message.
2. One or more RCPT commands identify the recipients of this message.
3. A DATA command transfers the message text.

To know more about SMTP mail server works please check Wikipedia link click here.