OSI/MHS Configuration and Management Manual

Introduction to OSI/MHS
OSI/MHS Configuration and Management Manual—424827-003
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X.400 Message Handling Systems
X.400 Message Handling Systems
An X.400 message handling system (MHS) has several types of components.
Figure 1-1 shows a high-level overview of an MHS.
An MHS user can be either a person or a computer process. A user can send a
message (the user is then referred to as an originator) or receive a message (the user
is then referred to as a recipient).
Each user has a user agent (UA). The user agent is an application process that helps
the user prepare messages. A remote user agent is a UA that runs on a system or
device other than the one where OSI/MHS is located. A local user agent is a UA that
runs on the same system as OSI/MHS. The UA interacts with the message transfer
system (MTS) or a message store (MS) to submit and deliver messages on behalf of a
single user.
The MTS contains message transfer agents (MTAs). MTAs work together to transfer
messages and deliver them to the intended recipient. Messages are submitted to the
MTS through a submission protocol and leave it through a delivery protocol.
Figure 1-1. Overview of a Message Handling System
002VS T .VSD
Message Handling System
Messa ge Tran sfer System
User
MTA
MTA
UA
UA MTAMTA
UA
UA
MS
MS
User
User User