rDNS 
Actually no, sir. You removed the wrong sentence. According to RFC1912 an IP-address can only resolve into ONE hostname (which is logical, since otherwise it wouldn't be resolving to a name at all). That was exactly my point: The RFC is this strict because it assures auth options, like whitelisting and such. Since only one name can resolve out of each IP-address, and unique IPv4 addresses are hard to come by these days, there is no way to keep combining the two. My statement was entirely correct, so I will reverse your stupid changes.