To block all subdomains of domain.com, the administrator should configure the domain.com address in the block list. This is because Umbrella automatically applies a left side and right side wildcard to every domain in a block or allow destination list. Therefore, adding domain.com to a block list will result in requests to domain.com or its subdomains, such as www.domain.com, being blocked. Adding a wildcard character (*) is not supported and will not work. Adding the *.com address in the block list will block all domains that end with .com, which is not the desired outcome. References: * Understanding Destination lists supported entries and error messages * Wildcards and Destination Lists