On Fri, Feb 03, 2012 at 12:21:28PM +0100, Kai Schaetzl wrote: > many "false" positives. There is no definitive RFC requirement that the > mapping has to match. But it's a standard security feature (on Solaris NFS server it was added around 1996, I think). Without the match I could set my servers IP address to be "mail.google.com". No one should believe me unless a forward lookup matches. It is commonly considered "broken" for rDNS to return a value that doesn't match forward DNS. > false positive ratio is very low. Certainly lower for me than Sorbs (threw > out Sorbs years ago). I, personally, use zen.spamhaus.org -- rgds Stephen