A text aimed at those with current or planned involvement in the management of X.400, including messaging managers, system or network planners and software developers. This book provides background knowledge of mailing systems and functionality as well as a grasp of how the underlying network operates. It explains the terminology and concepts of the standards. Because the standards are very abstract, the author has illustrated them with an overview of MAILbus 400 and Digital X.500, which are thorough and faithful implementations of the standards.