Gateway policy is a centralized set of rules enforced by an email security gateway before messages leave an organization. Instead of relying on each user to choose the right option, the gateway can automatically require encryption, block sensitive attachments, add disclaimers, or route mail through approved transport paths. This makes policy consistent across all outgoing mail and reduces the chance that staff accidentally send plain text or use the wrong protection method.
In cyber security, gateway policy matters because email is a common channel for data leakage and interception. Defenders use it to apply controls such as TLS requirements, content inspection, and message encryption based on sender, recipient, or content rules. Attackers may try to bypass it by sending through unmanaged mail services or by convincing users to forward data outside approved workflows. A well-designed gateway policy helps close those gaps by turning security decisions into enforced organization-wide controls.