>surely we in the IETF should be able to do better than to have our mail >servers filter incoming mail based on completely irrelevant criteria >like whether a PTR lookup succeeds! Spam filtering is sort of like chemotherapy, the difference between the good and the bad is pretty small, and the trick is to find measures that will kill the disease without killing the patient. It's entirely a matter of statistics, not fundamental design. I can assure you that in the outside world, the amount of legitimate mail that comes from no-PTR hosts these days is infinitesimal. It's one of the filtering rules with the lowest false positive rates. Other than temporary glitches like the 6-to-4 one, the only place where I see problems is from auld pharts like us whose mail systems have been working just fine since the 1980s, and who out of a weird sort of principle refuse to make changes to bring them in line with modern practice, even changes that are compatible with equally ancient STD documents. So, yeah, spam stinks, but it's not going away, and arguments that you shouldn't use a technique today because it didn't work in 1998 don't cut it. Regards, John Levine, johnl@xxxxxxxx, Primary Perpetrator of "The Internet for Dummies", Information Superhighwayman wanna-be, http://www.johnlevine.com, ex-Mayor "More Wiener schnitzel, please", said Tom, revealingly. _______________________________________________ Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf