Concept:SMTP is the standard protocol designed for sending and transmitting email messages over the internet.Explanation:Email transmission uses a dedicated protocol called Simple Mail Transfer Protocol, abbreviated as SMTP.SMTP handles the transfer of outgoing mail from a client to a server and between mail servers.The other options are unrelated: HTTP is used for web pages, DHCP assigns IP addresses, and IP is the internet addressing protocol.Therefore, the protocol used for email transmission is SMTP.Answer:D. SMTP