What protocol is commonly used for email transmission?

The correct answer is Simple Mail Transfer Protocol (SMTP). SMTP is specifically designed for sending emails over the internet. It is a communication protocol used for transferring electronic mail between servers. When an email is sent, SMTP handles the process by directing the email to the recipient's mail server.

In the context of email transmission, SMTP is essential because it establishes the rules for communication, ensuring that messages are sent efficiently and reliably. It operates over a network and uses a push model, where the email is pushed from the sender's server to the recipient's server.

The other options listed serve different purposes. File Transfer Protocol (FTP) is used for transferring files over the internet but is not designed for handling email transmission. Hypertext Transfer Protocol (HTTP) is utilized for transmitting web pages and facilitating communication between web browsers and servers, making it unrelated to email. Post Office Protocol (POP), while associated with email, specifically provides retrieval of emails from a server rather than sending them, and would typically work alongside SMTP to allow users to access their mail. Thus, SMTP stands out as the correct protocol for email transmission.