Describe the addressing system used by SMTP

Describe the addressing system used by SMTP.

The correct answer and explanation is :

Correct Answer:
SMTP (Simple Mail Transfer Protocol) uses email addresses to identify both the sender and recipient(s). The addressing format is local-part@domain, for example, user@example.com.

Explanation (Approx. 300 words):

SMTP (Simple Mail Transfer Protocol) is a protocol used to send emails over the Internet. The addressing system it uses is crucial to ensure that messages are delivered to the correct recipients. SMTP relies on email addresses to route messages between mail servers.

An email address consists of two parts, separated by the “@” symbol:

• Local-part: This identifies the specific user or mailbox on a mail server. It can include letters, numbers, and certain special characters.
• Domain: This identifies the mail server responsible for receiving emails for the user. It typically corresponds to a registered domain name, such as gmail.com or yahoo.com.

For example, in the email address john.doe@example.com:

• john.doe is the local-part.
• example.com is the domain.

When a user sends an email using an email client, SMTP contacts the Domain Name System (DNS) to resolve the recipient’s domain into an IP address of the destination mail server. It then initiates a connection to that server and uses the MAIL FROM and RCPT TO commands to transmit the sender’s and recipient’s addresses.

SMTP does not authenticate users based on email addresses alone—it only routes the message based on the addresses provided. This is why protocols like SPF, DKIM, and DMARC are often used alongside SMTP to help verify the legitimacy of email senders.

In summary, SMTP uses a simple, standardized addressing format—local-part@domain—to identify where emails are coming from and where they should be delivered. The domain portion ensures messages reach the correct server, while the local-part directs them to the correct user or mailbox within that server.