Milter-greylist

Over the last couple of days the amount of spam coming into our mailboxes has increased by at least 5 times. In trying to find the problem I see that every message, even spam messages, have this in the header...

X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.0.1 (mail.rlknight.com [172.16.88.3]); Sun, 12 Jul 2009 10:18:11 -0700 (PDT)

It looks like everything is IP whitelisted and no messages are being delayed and that has led to a huge increase in spam. I looked in the Greylist wiki and faq but couldn't find anything that looked related to this problem. How can I get milter-greylist to start delaying messages again?

Thanks,
Rick Knight