A company has publicly hosted web applications and an internal Intranet protected by a firewall. Which technique will help protect against enumeration?

Rejecting invalid SMTP email addresses reduces email harvesting but does not protect against DNS or network enumeration of internal hosts.

Allowing full DNS zone transfers actively enables enumeration by exposing all DNS records to any requesting client, which is the opposite of protection.

By removing A records for internal hosts from publicly accessible DNS servers, administrators prevent external attackers from mapping internal IP addresses through DNS enumeration techniques. Without these records, tools like nslookup, dig, or zone transfer attempts cannot reveal the internal network structure. This is a foundational DNS hardening practice for split-horizon or public-facing DNS configurations.

Enabling null session pipes on Windows systems exposes user, group, and share information to unauthenticated users, increasing enumeration risk rather than reducing it.