int checkdnsrr(string host, string [type]);
Searches DNS for records of type type corresponding to host. Returns true if any records are found; returns false if no records were found or if an error occurred.
type may be any one of: A, MX, NS, SOA, PTR, CNAME, or ANY. The default is MX.
host may either be the IP address in dotted-quad notation or the host name.