This paper presents CARE, an autonomous email reputation system based on inter-domain collaboration. Within the framework of CARE, each domain independently builds its reputation database based on both the local email history and the information exchanged with other collaborating domains. CARE examines the trustworthiness of the email histories obtained from collaborators by correlating them with the local email history. To validate the efficacy of CARE, we have analyzed real email logs, conducted a DNS-based estimation experiment, and performed a series of simulations. Our experimental results show that CARE can effectively improve the reliability and performance of email systems.