ITPEC FE Subject A April 2025 Question 33

It checks the sending server's IP address against the domain's DNS information — SPF is a sender domain authentication mechanism for email.

The owner of a domain publishes an SPF record, a DNS TXT record listing the IP addresses of the mail servers allowed to send mail for it. A receiving server takes the domain from the envelope sender (MAIL FROM), looks up that record in DNS, and checks whether the connecting server's IP address is on the list. On a mismatch the message can be rejected or marked as suspect.

Answer (c)

Why not others:

• •(a) — a department's rule about who sends mail is an internal policy, not an email protocol
• •(b) — mail from a spoofed address is the threat SPF is designed to detect, not SPF itself
• •(d) — addressing one recipient instead of many has nothing to do with sender authentication

Key rule: SPF authenticates the sending server's IP address, DKIM signs the message with a key published in DNS, and DMARC tells receivers what to do when these checks fail.

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