A request message is generated with a trusted network entity executing trusted code on a first network layer. The request message to target a non-trusted network entity executing non-trusted code on a second network layer. The request message is transmitted from the trusted network entity to the non-trusted network entity through at least a policy enforcement entity. The policy enforcement entity applies one or more network traffic rules to enforce a unidirectional flow of traffic from the first network layer to the second network layer. A response check message is generated with the trusted network entity. The response check message to determine whether response information is available on the non-trusted network entity in response to the request message. The response check message is transmitted from the trusted network entity to the non-trusted network entity through at least the policy enforcement entity. The response check message to determine whether the response information is stored in a conceptual mailbox on the non-trusted network entity.