Which of the following is a feature of IPsec?

IPsec is a comprehensive suite of protocols that is specifically designed to secure Internet Protocol (IP) communications by providing both authentication and encryption for IP packets. The primary function of IPsec is to protect the integrity, authenticity, and confidentiality of the data being transmitted over an IP network.

When IP packets are encrypted using IPsec, it ensures that even if the data is intercepted during transmission, it remains unreadable to unauthorized parties. Additionally, the authentication features of IPsec verify that the data has not been altered in transit and affirm the identity of the sender.

This combination of encryption and authentication is fundamental to enhancing network security and is widely used in Virtual Private Networks (VPNs) and other secure communication channels. The other options do not accurately represent the functions of IPsec; for example, IPsec does not operate at the application layer, it is not limited to just authentication, nor is it solely focused on email encryption.