IEEE 1224.1-1993

This standard defines two application program interfaces (APIs) of architectural importance in the construction of message handling systems (MHS). It defines an X.400 Application API that makes the functionality of a message transfer system (MTS) accessible to a message store (MS) or user agent (UA), or the functionality of a simple MS accessible to a UA. It also defines an X.400 Gateway API that divides a message transfer agent (MTA) into two software components, a mail system gateway and an X. 400 gateway service. The two interfaces support Message Access (MA), Message Transfer (MT), and Interpersonal Messaging (IM). MA is the conveyance of information objects between the MTS and one of its users, and thereby among its various users. MT is the conveyance of such objects between the MTAs that make up the MTS. IM is the MA and MT application in which the contents of messages are electronic memos. The interfaces address the operational requirements of these activities; they do not address their system management requirements, for example, those for security. NOTE -- Of the many applications of MA and MT, IM is singled out by this standard only because it is singled out by X.400 itself. (X.400 highlights IM for purely historical reasons.) The use of the interfaces is not limited to IM. Since they permit the contents of messages to be arbitrary binary data, the interfaces are germane to all applications, e.g., electronic data interchange (EDI). Henceforth, the following terms are used consistently as indicated. The terms MA interface and MT interface denote the X.400 Application API and the X.400 Gateway API, respectively. The term interface denotes either interface without distinction, or one interface in particular. If the latter, which interface is meant will be clear from the context. The term service denotes software that implements an interface. A service that implements the MA interface realizes the MTS. A service that implements the MT interface realizes an X.400 gateway service. The term client denotes software that uses an interface. A client that uses the MA interface realizes a UA or an MS. A client that uses the MT interface realizes a mail system gateway. NOTE -- The MA interface does not provide the functionality of the MS Abstract Service of X.400 (its P7 protocol), although it can be viewed as providing a small portion of it. The functionality of P7 is outside the scope of this standard. The message storage and retrieval capabilities of a mail system are among its most important product-differentiating aspects.