What must be configured to provide Internet access to each site's Client Access servers across multiple Active Directory sites?

To provide Internet access to each site's Client Access servers across multiple Active Directory sites, configuring the external URL for each Client Access server is crucial. The external URL serves as the point of access for clients outside the organization's network. This configuration ensures that clients can connect to the servers using a consistent and accessible address, facilitating proper communication and service access.

Each Client Access server must have an appropriately set external URL to allow users, devices, and applications to reliably reach the services provided by Exchange. This enables functionalities such as Outlook on the web, mobile access, and other client connectivity features, all of which rely on being able to resolve the external URL to the correct public-facing address.

In contrast, while Internet Protocol settings, firewall settings, and VPN access points play roles in the broader network configuration, they are not specific to ensuring clients can access the Exchange services directly via the Client Access servers. These aspects may need to be managed for overall secure communications and connectivity, but the direct provision of internet access from the perspective of client connectivity hinges on the correct external URL configuration for each server.