Which ensures authentication of an email?

Authentication is the process of verifying the identity of a sender or user. In the context of email, it ensures that the message truly originated from the claimed sender and has not been altered. The correct answer is Digital Signature.

• Digital Signature: A digital signature uses cryptographic techniques to provide authenticity, integrity, and non-repudiation for an email. The sender signs the email with their private key, and recipients use the sender's public key to verify the signature. This process confirms the sender's identity and guarantees that the email content has not been tampered with since it was signed.
• Password: A password authenticates a user to an email *account* or service (e.g., logging into Gmail), but it does not authenticate individual email messages sent from that account.
• Encryption: Encryption protects the *confidentiality* of an email, making its content unreadable to unauthorized parties. While vital for security, encryption alone does not verify the sender's identity or ensure message integrity.
• Spam alert: A spam alert is a system designed to identify and filter unsolicited or malicious emails. It's a filtering mechanism, not a method for authenticating the sender of a legitimate email.