ISO/IEC 10021-2:2003 ITU-T Rec. X.402 (1999) defines the overall architecture of the Message Handling System (MHS) and serves as a technical introduction to it. ISO/IEC 10021-2:2003 ITU-T Rec. X.402 (1999) first presents abstract models of Message Handling, then specifies how one can configure the MHS to satisfy any of a variety of functional, physical, and organizational requirements. It describes the naming and addressing of users and distribution lists and the routing of information objects to them. It describes the uses the MHS may make of the Directory and how the MHS is realized by means of OSI. The conventions used in the definition of the abstract services provided by MHS components are defined. Annexes provide important supplemental information.