Domain Name System Security Extensions (DNSSEC) is a feature added to DNS standards that ensures that the DNS records served to clients have not been tampered with in-transit. In other words, enabling DNSSEC ensures that the server you intend to send your employees and clients is the server they are sent to.
For those not familiar, DNS is the service that translates your domain name (e.g. www.example.com) to your server’s actual IP address (e.g. 126.96.36.199). DNS exists, primarily, to relate easy-to-remember names to IP addresses. Enabling DNSSEC ensures that no one can get in the middle of that translation between name and IP to modify the IP address, thereby sending your users or clients to a malicious server.
Enabling DNSSEC is usually free and performed differently by each DNS provider. Below is a short list of tutorials from various DNS providers to help get you started.