LambdaLabTM
Computer Networks · Class 12 · Network Protocols · Email
networksprotocols⏱️ 6 min read

SMTP

🎬 This chapter has a 10:53 video: Network Protocols →

You press Send, and a second later the email is gone. It did not go straight to your friend’s phone. It went to a mail server, then to another mail server, and it is waiting there. Every hop of that sending uses one protocol.

1What SMTP is

SMTP
SMTP stands for Simple Mail Transfer Protocol. It is the protocol used for sending email: from the sender’s mail app to the mail server, and from one mail server to another, until the mail reaches the receiver’s mailbox.

A mail server is a computer that keeps email for the people with addresses on it — everyone @example.org uses the mail server of example.org. Each person has a mailbox on it.

Sending one email

Play the story, or step through it. Drag sideways to turn.

Press ▶ Play to send Priya's email with SMTP.

Addresses use example.com and example.org, domains kept for examples. priya@example.com belongs to nobody.

2How SMTP sends a mail

  • SMTP reads the header of the email — like the address on an envelope — and does not look at what the message says.
  • The mail, with its header and body, joins a queue of outgoing mails.
  • The SMTP sender takes mails from the queue and sends them on. Each time it delivers to one receiver, it removes that address from the mail’s list of destinations. When every receiver has it, the mail leaves the queue.
  • The SMTP receiver at the other end accepts each mail and places it in the right person’s mailbox.

Think of the post office

You drop a letter in the post box (your mail server). The post office reads only the address on the envelope, and carries the letter to the post office in your friend’s town (their mail server), which puts it in their letter box. It stays there until your friend comes to collect it — and collecting is a different job, done by POP3.
“Send and receive email” in an MCQ
SMTP carries the mail all the way to the receiver’s mail server, so the receiving server uses SMTP too. If a question asks which protocol is used to send and receive email and SMTP is the only email protocol offered, choose SMTP. If it asks which one retrieves mail from the server to your device, choose POP3.

3From the board papers

1
Expand the term SMTP. What is the use of SMTP?CBSE sample paper 2024-25 · the full form alone in sample paper 2022-23
2 marks
▶Show the answer

Simple Mail Transfer Protocol. SMTP is used for sending emails from the client to the server — CBSE’s marking scheme answer — and on from mail server to mail server.

2
Which protocol out of the following is used to send and receive emails over a computer network? (a) PPP (b) HTTP (c) FTP (d) SMTPCBSE board exam 2024
1 mark
▶Show the answer

(d) SMTP — the only email protocol among the four.

4Check yourself

Quick Check

Priya's mail server has delivered her email to one of its two receivers. What happens to the mail in the outgoing queue?

Quick Check

Which part of an email does SMTP use to deliver it?

← Previous
📁 FTP
Next →
POP3 📥