SMTP is one of the most common and popular protocols for email communication over the Internet and it provides intermediary network services between the remote email provider or organizational email server and the local user accessing it.

SMTP is generally integrated within an email client application and is composed of four key components:

1. Local user or client-end utility known as the mail user agent (MUA)
2. Server known as mail submission agent (MSA)
3. Mail transfer agent (MTA)
4. Mail delivery agent (MDA)

SMTP works by initiating a session between the user and server, whereas MTA and MDA provide domain searching and local delivery services.