What are the two mail protocols used for delivery of messages, and how do they function?

What will be an ideal response?

After an email message arrives at the destination email server, it remains there until the recipient requests delivery. The recipient's email server uses one of two protocols to deliver the message: POP3 (Post Office Protocol, version 3) or IMAP4 (Internet Message Access Protocol, version 4). Using POP3, email is downloaded to the client computer and, unless the default setting is changed, the email is then deleted from the email server. Using IMAP, the client application manages the email stored on the server.