Which protocol is used primarily for email transmission?

SMTP, or Simple Mail Transfer Protocol, is the primary protocol used for sending and transmitting email across networks. It operates over the TCP/IP protocol suite and is designed specifically for sending messages between email servers. When you compose an email and hit "send," SMTP is responsible for routing that email to the recipient's mail server.

While other protocols like POP3 (Post Office Protocol version 3) and IMAP (Internet Message Access Protocol) are used for retrieving and managing emails from a server, they are not responsible for the transmission of emails. FTP (File Transfer Protocol) is used for transferring files between computers on a network, and HTTP (Hypertext Transfer Protocol) is used for transferring web pages and data on the internet. Therefore, the distinction lies in SMTP's role in the sending process, making it the correct choice for email transmission.