SMTP is used widely to send and receive emails over a small network. The protocol uses the Sender-SMTP process to send emails and the Receiver-SMTP process to receive emails. This makes SMTP a client-server-based protocol that runs over port 25
.
Typically, an SMTP channel for mail transfer is created through a successful TCP three-way handshake followed by a series of SMTP packets:
In our lab, we have an SMTP server configured at IP 192.168.1.105
and a client at IP 192.168.1.104
. The client will request the server to sends an email to an address known to the client. The server will respond to this request with numerical code, followed by a brief response parameter.