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

The protocol typically used by email clients to retrieve messages from a server is POP3. This protocol, which stands for Post Office Protocol version 3, is designed specifically for this purpose. When a client utilizes POP3, it connects to the mail server, retrieves emails, and then usually deletes them from the server. This is beneficial for users who prefer to manage their emails locally on their devices, though it can also limit access to the messages from multiple devices.

While IMAP is also used for retrieving messages from a server, it differs in that it allows users to view and manage their emails directly on the server without removing them. This enables access to the same email account from multiple devices. SMTP, on the other hand, is primarily used for sending emails, not retrieving them. HTTP is a protocol for transferring web pages and is unrelated to email message retrieval. Therefore, focusing on the specific design and function of POP3 clarifies why it is the appropriate choice for this question.