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 a hierarchical addressing system based on email addresses, which follow the format user@domain. The address identifies both the recipient (user) and their mail server (domain).

Explanation (300 words):
SMTP (Simple Mail Transfer Protocol) is the standard protocol used for sending email across the Internet. The addressing system used by SMTP is based on email addresses, which are globally unique identifiers in the format: username@domain.

In this format:

• username is the local part, identifying the recipient’s mailbox on the mail server.
• domain is the domain part, identifying the server that handles email for that user.

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

• "jane.doe" is the user’s mailbox.
• "example.com" is the domain that hosts the mailbox.

SMTP relies on this addressing system to route email messages correctly from the sender to the recipient. When a message is sent, the sending SMTP server looks at the domain part of the recipient’s email address. It uses the Domain Name System (DNS) to find the Mail Exchange (MX) records associated with that domain. These records point to the recipient’s mail server.

Once the appropriate mail server is located, the SMTP server establishes a connection and transfers the message using a set of standard SMTP commands like HELO, MAIL FROM, RCPT TO, and DATA. The RCPT TO command specifically uses the full email address of the recipient to direct the message.

SMTP supports multiple recipients, and each address is processed individually. The use of a standard format (user@domain) ensures interoperability across networks and email providers globally. This hierarchical and domain-based system is essential for ensuring messages are delivered accurately and securely across the vast and decentralized infrastructure of the Internet.