Figure .F.:1/X.402 The Message Handling Environment
7.1.1 The Message Handling System
The principal purpose of Message Handling is to convey information objects from
one party to another. The functional object by means of which this is
accomplished is called the .I.gl:Message Handling System; (.I.ab:MHS;).
The MHE comprises a single MHS.
7.1.2 Users
The principal purpose of the MHS is to convey information objects between users.
A functional object (e.g., a person) that engages in (rather than provides) Message
Handling is called a .I.gl:user;.
The following kinds of user are distinguished:
a) .I.gl:direct user;: A user that engages in Message Handling by direct use of
the MHS.
b) .I.gl:indirect user;: A user that engages in Message Handling by indirect use
of the MHS, i.e., through another communication system (e.g., a postal system or the
telex network) to which the MHS is linked.
The MHE comprises any number of users.
7.1.3 Distribution Lists
By means of the MHS a user can convey information objects to pre-specified groups
of users as well as to individual users. The functional object that represents a pre-specified group of users and other DLs is called a .I.gl:distribution list;
(.I.ab:DL;).
A DL identifies zero or more users and DLs called its .I.gl:members;. The latter
DLs (if any) are said to be .I.gl:nested;. Asking the MHS to convey an information
object (e.g., a message) to a DL is tantamount to asking that it convey the object to
its members. Note that this is recursive.
The right, or permission, to convey messages to a particular DL may be controlled.
This right is called .I.gl:submit permission;. As a local matter the use of a DL can
be further restricted.
The MHE comprises any number of DLs.
Note A DL might be further restricted, e.g., to the conveyance of messages of a
prescribed content type.
7.2 Secondary Functional Objects
The MHS comprises the Message Transfer System, user agents, message stores, and
access units. These secondary functional objects interact with one another. Their types
