Which protocol is primarily responsible for routing email messages between mail servers?

• A. SMTP
• B. POP3
• C. IMAP
• D. FTP

Answer: (A)

SMTP is the protocol used to route and transfer email messages between mail servers. It handles the handoff of messages from the sender’s server to the recipient’s server (and any relays in between), guiding how the message is relayed across servers. It operates independently of the end-user’s mailbox access, which is handled by other protocols. POP3 and IMAP are for retrieving and managing email on a client, not for server-to-server delivery, while FTP is simply a file transfer protocol and not used for email routing. In practice, a message is handed off between servers using SMTP after DNS MX records point to the destination server, making SMTP the correct choice for inter-server routing.