SMTP's lack of encryption primarily affects which aspect of email security?

• A. Integrity of messages.
• B. Sender authentication.
• C. Confidentiality of message content.
• D. Non-repudiation.

Answer: (C)

When SMTP is used without encryption, the actual text of the message travels in clear, readable form. Anyone who can observe the network traffic—intermediaries, network admins, or attackers on the path—can read the body, subject, and any attachments. That direct exposure is a breach of confidentiality, since the content is not protected from eavesdropping. Other security aspects rely on different mechanisms: authenticity and non-repudiation require digital signatures and proper authentication methods, while integrity can be ensured by secure transport or signing, but the primary risk created by the lack of encryption is that the message content is exposed in transit.