Reputation Management is hot topic and I worked on SERMA reporting last year (search engine reputation management) but I never worked with anything that does that for Email.

But now Email accreditation provider Habeas just launched a new email reputation database, SenderIndex, which will make use of data and ISP relationshipsdeveloped via Habeas SafeList whitelist, reports ClickZ.

"The SafeList is a whitelist used by more than 130,000 ISPs and message filtering companies to aid in filtering e-mail based on Habeas’ certification of the senders meeting its criteria for good sending practices. Those same ISPs provide data back to Habeas to help it maintain the SafeList, and now the SenderIndex. "

"…Senders who fail the tests miserably are put on a Block List, and receivers are advised to block those messages with confidence that the false positive rate will be very low. The rest of the senders fall into the Grey List, and receivers are advised to use other means to filter or block those messages. "

So now I get an idea of how an email address can suddenly get blocked.