On Fri, 23 Sep 2011 20:50:27 +0200, Alessandro Vesely said:
Most SMTP servers duly lookup the client's IP and annotate the
resulting name as comment in Received fields. However, I don't recall
denying SMTP access based on the "iprev" test (as RFC 5451 named it.)
Was it ever à la mode to do so?
At one time, the net was still small enough that it was a safe assumption that
if you got mail from an IP address that didn't have a valid rDNS, it was (a) a
rare event because (b) a missing rDNS meant the provider was asleep at the
wheel.
Now-a-days, most providers have automatic provisioning systems that assign
rDNS for customer addresses, so most of Vint Cerf's famous 140 million
compromised machines have an rDNS entry, which means it's not that
effective anymore.
(What *is* used a lot today is 'rDNS looks like a customer cablemodem/adsl
connection')
True statement on both accounts. I'd add to it, that invalid rDNS is still a
viable anti-abuse mechanism. There are plenty of compromised machine operators
that are "asleep at the wheel." Checking rDNS scrapes off that chaff.