The correct answer is A.
IMAP4.IMAP4 is an application layer protocol which is used to receive the emails from the mail server. It is a more modern and secure protocol than POP3, which is the other main protocol used for email retrieval. IMAP4 allows users to access their email from multiple devices and to keep their email on the server until they delete it.
TCP is a transport layer protocol that is used to establish a connection between two hosts on a network. It is a reliable protocol that ensures that all data is transmitted correctly. HTTP is a hypertext transfer protocol that is used to transfer data between a web server and a web browser. It is a stateless protocol, which means that each request from the client is independent of the previous requests.
TCP3 is not a valid protocol.