Which protocol is typically used by email clients to download messages from a mail server?

The protocol typically used by email clients to download messages from a mail server is POP3. This stands for Post Office Protocol version 3. POP3 is designed specifically for retrieving emails from a remote server to a local email client. When users download their emails using this protocol, the messages are often stored locally and may be deleted from the server, which is particularly useful for those who want to access their emails offline.

IMAP, while also used for email retrieval, allows users to view and manage their emails directly on the server, which means the emails remain on the server unless explicitly deleted. SMTP, or Simple Mail Transfer Protocol, is actually used for sending emails, not downloading them. HTTP, which stands for Hypertext Transfer Protocol, is used primarily for transmitting web pages and is not relevant for email downloading. Therefore, POP3 is the correct choice for downloading messages from a mail server to a client.