A server system can include an internal computer network including at least one client server configured to establish a data transfer connection to an external computer network, and at least one proxy server system positioned between the internal computer network and the external computer network. The proxy server system can include a proxy server positioned between a first firewall and a second firewall, where the first firewall is positioned between the first proxy server and the internal computer network, and the second firewall is positioned between the proxy server and the external computer network. The server system can develop and maintain a proxy server system that includes a whitelist of sites deemed necessary and/or desirable for system operation. The whitelist can be updated as a user works with and uses the system. Such updates can take place continuously in real or near-real time or periodically as frequently as desired. A single party can be the only entity that can update the whitelist, ensuring the whitelist contains all required sites. Whitelist updates can be automatically delivered to all proxy instances as the whitelist changes over time.