What is the primary function of a Domain Controller in a network?

The primary function of a Domain Controller in a network is indeed to manage user accounts and security policies. This role is critical within Windows domains and involves the authentication and authorization of users and computers. The Domain Controller means that it stores user account information, including passwords, and enforces security policies for the domain.

When a user logs in to a network, the Domain Controller verifies the credentials and determines what resources the user is allowed access to, handling permissions and group policies. Additionally, the Domain Controller facilitates centralized management of user profiles and security settings, which helps maintain the network's security integrity and overall efficiency.

In contrast, other options pertain to different network functions. File storage and resource sharing are usually handled by file servers, the main internet gateway’s purpose is to route traffic between the local network and the internet, and email services are typically managed by dedicated mail servers. Each of these serves a unique function within the network, but they do not fulfill the role that a Domain Controller does.