The Value of a Good Name: This is sort of a global whitelist, really.
“Your reputation precedes you. This is the idea behind a new weapon in the war on spam and e-mail overload from IronPort Systems: reputation filtering. The IronPort C60 Messaging Gateway appliance controls the flow of e-mail coming into your network based on the reputations of the senders. Reputations are primarily established using data collected from more than 11,000 organizations that participate in IronPort’s SenderBase network.”