Randy Bush wrote:

this is what i call shooting in the dark. what are OBJECTIVE METRICS? for example, can operators measure and publish alpha and beta error rates on a selection of sites of different flavors so we can decide when they are low enough for our flavor of site to enable rdns filters?

The only usable metric you have, Randy, is the amount of collateral damage you would face on your network if you turned on rDNS. Trust me, the error rates on sites would vary widely, especially because you cannot assume a standard / uniform population of people sending mail to these sites. People who mail IETF lists, and people in asia, sending mail to a local list server in the rDNS-less desert that is some parts of APNIC land, might have completely different perceptions on the issue. Now, from your logs, just how much legitimate mail do you get that comes from an IP without PTR RR, and how much is that expressed as a percentage of legitimate incoming mail to your lists? How much is that as a percentage of spam inbound to your list [to be fair, let's make it "spam that would not have been stopped by your other filters]? srs