Application layer protocol

Question

Which of the following Application Layer Protocol cannot be used between mail server and receiver’s client machine?

• A. SMTP
• B. HTTP
• C. POP3
• D. IMAP4

Comments

HTTP is used for viewing the mails in the web browser and so it cant be used btw the mail server and reciever's client machine.

Answer 1

The Internet Message Access Protocol (IMAP) is a mail protocol used for accessing email on a remote web server from a local client. IMAP and POP3 are the two most commonly used Internet mail protocols for retrieving emails. Both protocols are supported by all modern email clients and web servers.

SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in sending and receiving e-mail.

HTTP is used for viewing the mails in web browser. Therefore, HTTP  cannot be used between mail server and receiver’s client machine.

Comments

If you consider all the cases.. i think SMTP should be the answer. @Sandy Sharma

is right. We need to consider push-pull scenarios. By the way SMTP is becoming obsolete nowadays whereas HTTP is gaining dominance. eg- Gmail.

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@Sandy Sharma True. In terms of PUSH and PULL, SMTP cannot be used between mail server and receiver's client machine coz It is dedicated PUSH protocol. 

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but similarly can we use pop and imap as pull protocol??

Answer 2

Ans: A) SMTP

SMTP is a push protocol which is used for sending mail. Sender uses SMTP to push his email to be sent to the mail server. 

Note: SMTP can be used between Sender and Mail Server or Mail Server to Mail Server but not between Receiver and Mail Server.

For receiving mail a pull protocol is required either IMAP or POP can be used.

So answer is SMTP since it can’t be used in case of Receiver.

Ref: https://www.gatevidyalay.com/simple-mail-transfer-protocol-smtp-protocol/