Which protocol is used to send email messages from a mail client to a mail server?

The protocol used to send email messages from a mail client to a mail server is Simple Mail Transfer Protocol (SMTP). This protocol is specifically designed for the transmission of email. When a user composes an email and clicks "send," the mail client communicates with the mail server using SMTP to relay the message to its destination. SMTP is essential for ensuring that the email is properly formatted and routed to the intended recipient's email server.

In contrast, the other options serve different purposes. Hypertext Transfer Protocol (HTTP) is primarily used for transferring web pages and other web content over the internet. File Transfer Protocol (FTP) is used for transferring files between computers on a network. Internet Message Access Protocol (IMAP) is utilized for accessing and managing emails stored on a mail server but is not responsible for sending emails. Hence, SMTP is uniquely suited for the task of delivering email messages from clients to servers.