Which protocol is the standard for sending emails between servers?

• A. Simple Mail Transfer Protocol (SMTP)
• B. Hypertext Transfer Protocol (HTTP)
• C. File Transfer Protocol (FTP)
• D. Domain Name System (DNS)

Answer: (A)

Sending emails between servers is handled by SMTP, a TCP-based protocol built specifically for relaying messages from one mail server to another. It defines the dialogue between servers—how a server introduces itself, how the sender and recipient are specified, and how the message content is transferred. This makes SMTP the standard way mail is moved across the Internet from server to server. In practice, the submission from a user’s mail client to a mail server often uses SMTP on a submission port, while the delivery path between servers continues to use SMTP. Retrieval from a mailbox to a client uses other protocols like POP3 or IMAP, not SMTP.

The other options don’t fit because HTTP is for web pages, FTP is for file transfer, and DNS maps domain names to IP addresses. None of them are designed to transport mail messages between mail servers.