The present document specifies requirements for achieving interoperability between the Registered Electronic Mail systems that are compliant with TS 102 640 (REM henceforth) specification and systems that are compliant with "Business Document Exchange Network service metadata and transport specification" (BUSDOX henceforth). 
The approach used for this purpose is to define all the necessary mappings between the two specifications taking into account also the objective to maintain and preserve the main advantages and positive features present in both the realities as pursued in the Technical Specifications.