A wildcard DNS is used to share some files among the domin and its sub-domins. A wildcard DNS record may be a record in an exceedingly DNS zone that may match requests for non-existent domain names. This server lacks the wildcard DNS entry. It narrows down the addresses at which the organisation hosts machines. It significantly reduces the preparatory work necessary to locate machines, map the topology and launch an attack.
*.example.com. 3600 IN MX 10 host1.example.com.
The attacker can attack the domain and its sub-domains.