ITPEC FE Morning April 2023 Question 45
When a sender from domain A sends an e-mail to a recipient in domain B, which of the following is used by the mail server in domain A for authenticating the sender?
Explanation
SMTP-AUTH — the sender's own mail server checks who is submitting the message before relaying it to domain B.
Sending mail uses SMTP: the sender's mail client submits the message to the domain A server, which relays it to the domain B server. SMTP-AUTH is an SMTP extension in which the client logs in with a user ID and password before the server accepts the message. It stops outsiders from using the server as an open relay for spam.
Answer (d)
Why not others:
- •(a) APOP — a POP3 login that sends a challenge-response digest instead of a plain-text password; it is used when the recipient collects mail, not when the sender sends it
- •(b) POP3S — POP3 over SSL/TLS, which encrypts the recipient's download from the mailbox
- •(c) S/MIME — signs and encrypts the message content end to end; the recipient can verify the signature, but the mail server does not use it to authenticate the sender
Key rule: Authentication on the sending side belongs to SMTP (SMTP-AUTH); authentication on the receiving side belongs to POP3 or IMAP (APOP, POP3S, IMAPS).
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