This document specifies the information exchanges between various parties\' infrastructures that take place in support of DPM applications. It complements standards that address the design, security, applications and readability of Digital Postage Marks. The following items will be addressed by this document: - identification of parties participating in exchanges of information described by this document; - identification of functions (interactions, use cases); - definition of parties’ responsibilities in the context of above functions; - definition of messages between parties: message meaning and definition of communication protocols to support each function; - definition of significant content (payload) for each message; - security mechanisms providing required security services, such as authentication, privacy, integrity and non-repudiation. This document does not address: - design of DPM supporting infrastructure for applications internal to providers and carriers; - design of DPM devices and applications for applications internal to end-users. NOTE Although there are other communications between various parties involved in postal communications, this document covers only DPM-related aspects of such communications.