E L Castelli of LashBack, provider of unsubscribe services and sender scoring based on unsubscribe performance, blogs about Email Reputation Silos

Musings of a VC in NY has two pieces on email reputation: November 2004 opening up discussion of some good Internet reputation systems (not limited to email) and a post recognizing Sender Score's announcement at the beginning of July 2005

ReturnPath's CEO Matt Blumberg posts about Sender Score June 2005

ZDNet: Mail Cruncher trust-sifts spam from September 2004 excerpt "The Outbound Index, developed by Server Authority, is based on the premise that spammers tend to hide and move, whereas legitimate businesses tend to be stable and clearly identifiable. The service sorts e-mail based on factors such as domain age, relationships between server and domain, and sender stability."   more »