We've been refusing mail based on this stupid error for a year and a half (local rule) and no false positive has ever come to attention. The volume averages about 50,000 a day here. Yesterday it was 72,000 from 69.16.199.0/24. It comes from 1 to 3 IP subnets each day, changing daily, except that the spammer does not send on Sundays. I agree that many of them hit no other rule.
-- Joseph Brennan Lead, Email and Systems Applications
