Which of the following protocols is used to download messages from an email server?

HTTP (Hypertext Transfer Protocol) is used for transmitting web pages and data over the internet, not specifically for downloading email messages.

IMAP (Internet Message Access Protocol) is also used for accessing email messages on a server, but it typically keeps messages on the server and synchronizes them across multiple devices, rather than primarily downloading and removing them.

HTTPS (Hypertext Transfer Protocol Secure) is the secure version of HTTP, primarily used for secure web communication, not for downloading email messages.

POP3 (Post Office Protocol version 3) is designed to allow an email client to retrieve email messages from a mail server. When a client connects via POP3, it typically downloads all messages from the server to the local device and, by default, often deletes them from the server.