Comprehensive and Detailed Explanation From Exact Extract:

Non-repudiation ensures that a sender cannot deny sending a message. Digital signatures provide non-repudiation because they use the sender’s private key, which only the legitimate owner possesses. When the email recipient verifies the digital signature using the sender’s public key, it proves the email was sent by the true owner of the private key and has not been altered.

Confidentiality (B) ensures information is protected from unauthorized access and is usually achieved through encryption. Integrity (C) ensures data has not been modified, while authentication (D) verifies the identity of a user. Although digital signatures also support integrity and authentication, the specific property that prevents denial of sending the email is non-repudiation.

Security+ SY0-701 highlights digital signatures as a cryptographic mechanism used for authentication, integrity, and non-repudiation, especially in email security, PKI systems, and secure messaging.

Thus, the correct answer is Non-repudiation.