What is one function of a firewall?

A firewall's primary function is controlling network traffic. This system acts as a barrier between a trusted internal network and untrusted external networks, such as the internet. By establishing predetermined security rules, a firewall can allow or block traffic based on the specific criteria set by an organization. This is crucial in safeguarding sensitive data and ensuring that only legitimate traffic is permitted to pass through, thus protecting the internal network from unauthorized access and potential threats.

The other options do not align with the core functions of a firewall. For instance, while encryption is vital for securing data in transit, it is not a capability of a firewall. Backing up data is a separate process that involves creating copies of data to prevent loss, and monitoring email communications typically falls under the domain of email security solutions or data loss prevention tools rather than firewall technology.