> What is a valid rDNS? How is it set?
when you open an address in your browser a (forward) dns lookup will be initiated to get the server's ip address. A reverse lookup (rDNS) is the opposite. You query an ip address and get a fully qualified domainname back. Mailservers must have a matching forward and reverse dns, that means the domain in domain -> ip / ip -> domain queries must be the same. rDNS is set in the nameservers of the company that is responsible for your ip address (or ip net). Whereas you use resource records of type A for forward lookups, for rDNS you use PTR (Pointer) records. For more information you should search how DNS is working, for rDNS especially PTR / in-addr.arpa. and ip6.arpa. Best regards Gerald
