In this paper, we describe EMMA (E-Mail Management Assistant), an e-mail system that addresses the process of e-mail management, from initially sorting messages into virtual folders, to prioritizing, reading, replying (automatically or semi-automatically), archiving and deleting mail items. EMMA attains a high degree of accuracy on e-mail classification by using a rule-based approach known as Ripple Down Rules (RDR) as the basis of rule construction. In contrast to traditional rule-based systems, RDR systems provide extensive help to the user in defining rules and maintaining the consistency of a rule base, making EMMA easy to use. We discuss the results of evaluating the usability of EMMA on a trial of independent users.