Which of the following protocols is used for transferring electronic-mail…

Concept

An application-layer protocol defines the rules two machines follow to exchange a specific kind of data. For email, the job of carrying a mail message from one machine (the sender's mail server) to the next is the dedicated role of a single push protocol; the protocols used to read mail already sitting in a mailbox are separate and distinct.

Application

SMTP (Simple Mail Transfer Protocol) is the protocol designed precisely to push an outgoing mail message from one machine to another across the network. When a mail is sent, the sending server opens an SMTP connection to the receiving server and transfers the message to it. This is the exact action the question describes: moving an electronic-mail message from one machine to another.

Contrast

Distinguish it from the other options by what each is actually built to carry:

• HTTP carries web pages and resources between a browser and a web server. Reading email inside a browser (webmail) uses HTTP to the website, but the mail itself still travels between mail servers over SMTP.

• FTP carries files between computers on request; it has no role in routing mail.

• SNMP carries management and monitoring data about network devices such as routers and switches; it does not move mail.

Note also that POP and IMAP only retrieve mail already delivered to a mailbox; they do not transfer a message from one machine to the next. So among the choices, only SMTP performs the machine-to-machine mail transfer asked for.