E-mail services are essential in the Internet. However, the current e-mail architecture presents problems that open it to several threats. Alternatives have been proposed to solve some problems related to e-mail services, offering reliability and scalability to such systems. This work presents a distributed trust model, allowing to create dynamic and decentralized trusted server lists, through the exclusion of servers recognized as spreaders of malicious messages. The trust model uses a social network approach and defines strategies for trust information update, propagation, and storage. A prototype was built to evaluate the proposed model's effectiveness.