Consider the different activities related to email.
Which is the application level protocol used in each activity?
SMTP is a $push$ protocol used between the sender and sender's mail server.
POP is a $pull$ protocol used between receiver and the receiver's system.
HTTP is a $request-response$ protocol used mainly to access data on the world wide web.
Answer is (C)
Sender/Client send mail from client mailbox to server mail box with the help of SMTP protocol whereas Receiver or Server retrieve the mail from its mail box to reading using POP3 protocol.
When we want to take the help process to see email in browser in that case we HTTP.Because It creates beautiful page of mailbox with the help of process.
Sending an email - User agent
Message transfer agent -SMTP
Downloading an email from mail box - POP
Checking email in a web browser - HTTP
Client mail box to server = HTTP and SMTP( push protocol)
Downlode mail boc from server = POP and IMAP (Pull protocol)
Check in Browser = HTTP