Which of the following ensures a sender's authenticity and an e-mail’s confidentiality?

The process that ensures a sender's authenticity and an email's confidentiality is called encryption. Here are the steps:

1. Digital Signature: To ensure the sender's authenticity, a digital signature is used. This is a mathematical scheme for verifying the authenticity of digital messages or documents. It provides a layer of validation and security to messages sent through a non-secure channel.

2. Public Key Infrastructure (PKI): PKI is used to create, manage, distribute, use, store, and revoke digital certificates. This infrastructure includes a certificate authority (CA) that issues and verifies the digital certificates. The CA publishes the public key and verifies the identity of the user.

3. Secure/Multipurpose Internet Mail Extensions (S/MIME): This is a standard for public key encryption and signing of MIME data. S/MIME is used to encrypt the email and ensure its confidentiality. It uses a PKI to issue certificates.

4. Transport Layer Security (TLS): This is a protocol that ensures privacy between communicating applications and their users on the internet. When a server and client communicate, TLS ensures that no third party may eavesdrop or tamper with any message.

By using these methods, the sender's authenticity and the email's confidentiality can be ensured.