An open relay is a mail server configured to allow:

Question

Options

• AOpen system architecture
• BSending e-mail from untrusted networks
• CUn-authenticated e-mail
• DSMTP daisy chain allowing load sharing across multiple relays

• B
  87% (13)
• C
  7% (1)
• D
  7% (1)

Explanation

An open relay is an SMTP mail server that accepts and forwards email from any source, including untrusted or external networks, without requiring authentication from the sender - making B correct. This configuration is exploited by spammers to route bulk mail through a third-party server, obscuring the true origin.

• A (Open system architecture) is wrong - "open relay" is a specific mail server misconfiguration, not a system design philosophy.
• C (Un-authenticated email) is partially related but imprecise - the defining trait is accepting mail from untrusted networks, not merely lacking authentication (many internal servers accept unauthenticated mail legitimately).
• D (SMTP daisy chain for load sharing) describes legitimate mail relay clustering, which is the opposite scenario - controlled, trusted relaying, not open access.

Memory tip: Think of an open relay like an unlocked mailbox drop that anyone on the street can stuff with letters and have them forwarded - the "open" means open to outsiders (untrusted networks), which is what makes it a security vulnerability.

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