Which protocol is primarily used for transferring files over the Internet?

The protocol primarily used for transferring files over the Internet is File Transfer Protocol (FTP). FTP facilitates the uploading and downloading of files between a client and a server, making it a fundamental service for file sharing on the Internet. It operates using a client-server architecture, where the client can request files from the server or send files to it.

FTP allows users to authenticate themselves with a username and password, providing a secure method for transferring data. There are various modes of FTP, including plain FTP and secure variants like FTPS and SFTP, which further enhance its functionality for secure file transfer.

Other protocols listed serve different purposes: Simple Mail Transfer Protocol (SMTP) is designed for sending emails, Hypertext Transfer Protocol (HTTP) is primarily used for accessing web pages, and Post Office Protocol (POP3) is utilized for retrieving emails from a mail server. Each of these protocols plays a critical role in their specific applications, but none are primarily intended for file transfer in the way that FTP is.