Techniques for leveraging efficient metadata communications to improve domain name system (DNS) security are described. The DNS service uses a hash value to uniquely identify a client, and detect any change in metadata in order to keep policies up-to-date for the client. In an example method a first DNS query for a client device is intercepted. A cryptographic hash function is applied to metadata associated with the client device to generate a hash value. The hash value is added to an additional records section of the first DNS query to generate a second DNS query. The second DNS query is transmitted to a DNS service. The metadata associated with the client device is transmitted to the DNS service on an out-of-band encrypted channel. A DNS response, including the hash value, is received from the DNS service and transmitted to the client device.