We propose RepuScore, a collaborative reputation management framework over email infrastrucure, which allows participating organizations to establish sender accountability on the basis of senders’ past actions. RepuScore’s generalized design can be deployed with any Sender Authentication technique such as SPF, SenderID and DKIM. With RepuScore, participating organizations collect information on sender reputation locally from users or existing spam classification mechanisms and submit it to a central RepuScore authority. The central authority generates a global reputation summary which can be used to enforce sender accountability. We present the algorithms for reputation score calculation and share our findings from experiments based on a RepuScore prototype using a) our simulation logs and b) a 20 day log from a non-profit organization with five collaborating domains.