To create a DLP policy that specifically targets preventing the sharing of proprietary patent documents via email, the network administrator should use a custom policy template. A custom policy allows for the creation of tailored DLP rules and matching patterns based on the organization's specific requirements and data protection needs.
While regulatory compliance, acceptable use, and privacy protection policy templates may provide some predefined rules and patterns, they may not directly address the specific requirement of preventing the external sharing of proprietary patent documents. Therefore, a custom policy template would be the most suitable option as it provides flexibility in designing and implementing DLP rules specifically for the organization's unique data protection objectives.