Which protocol is used for sending email messages from a client to a server?

The protocol used for sending email messages from a client to a server is Simple Mail Transfer Protocol (SMTP). SMTP is specifically designed for the transmission of email messages across the Internet. When you send an email, your email client uses SMTP to relay the message to your designated email server. This protocol ensures that the email is properly formatted and sent to the correct destination address.

In contrast, other protocols listed serve different functions in the email process. For example, IMAP (Internet Message Access Protocol) and POP3 (Post Office Protocol, version 3) are used for retrieving emails from the server to the client, allowing users to access their inbox and manage their messages after they have already been delivered. HTTP (Hypertext Transfer Protocol) is primarily used for transferring web pages and is not specifically designed for email transmission.

Understanding the roles of these protocols is essential in networking, as it allows for better management of email communications and the architecture of email systems.