Which protocol is used to send email messages?

The correct answer is SMTP, which stands for Simple Mail Transfer Protocol. SMTP is specifically designed for sending emails across networks. It operates primarily over the TCP protocol and is responsible for the transfer of email messages from a sender's email client to a recipient's email server. SMTP facilitates the relaying of messages, often working in conjunction with other protocols like IMAP or POP3, which are typically used to retrieve emails from the server.

In contrast, the other options serve different purposes in networking. FTP, or File Transfer Protocol, is focused on transferring files between a client and a server, making it unrelated to the process of sending emails. HTTP, or Hypertext Transfer Protocol, is the foundation of data communication on the web, used for transmitting web pages and resources, but not for sending email messages. Lastly, SNMP, which stands for Simple Network Management Protocol, is utilized for monitoring and managing network devices, rather than handling email transmission. Thus, SMTP stands out as the protocol specifically dedicated to email communication.