One problem is when the piece of mail enters DCC (since Microsoft lists have a HUGE distribution their mail is pretty much guaranteed to be listed in DCC, as I understand it) and is scored an additional 2.2. As far as I can tell DCC does not distinguish between potential spam and ham, so while it's useful in most circumstances it's really easy to false-positive with this rule.
To be honest, I have by far more FPs from Razor than from DCC. Theoreticaly, on paper, DCC doesn't distinguish, but the system itself is more accurate and less prone to picking up legitamate mass-mailings.
