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A functional model.

An electronic mail system (MHS : Message Handling System) provides a generalized service of storage and routing (store-and-forward) to convey the messages between users of the electronic mail system.

The user of the electronic mail system can be a person or a data-processing application.

The System of Electronic mail operates in absence of point-to-point connection between the Originator and the Recipient of a message.

The MHS heart is the Message Transfer System (MTS) It is a service of general purpose communications, independent of the applications, and implementing store-and-forward service.

It is composed of message transfer agents (MTA) which cooperate to relay the messages until their destinations.

The MTS operates independently of the type of interchange required by the application and it is transparent compared to the nature of the contents of the message.

An MHS direct user reaches MHS services through an User Agent (UA ) - it is an application which interacts with the MTS to subject and receive the messages.

The basic service of X400 electronic mail provides the notification of message not given. When a message cannot be given to a recipient an opinion of not given is generated and turned over to the transmitter.

The service of electronic mail proposes as optional service the generation of opinion of distribution. If the transmitter of a message asks for an defendant of successful handing-over, a report of handing-over is turned over to the transmitter by the MTA which gave the message.

Messages can be transmited directly by MTS to the UA recipient or in an alternative way can be given to the equivalent of a mailbox which makes it possible to store the messages(MS: Message Store).

MS often co-resides with the MTA which serves it. Using an MS to take delivery of the messages makes it possible the UA not to have a process with the listening which waits to take delivery of the messages.

MS can also subjects and transmits the messages instead of the UA, and notifies to the UA the hour handing-over of the message.

The structure of a message MHS consists of an envelope and contents.

As for a postal mail, the envelope represents the information required by the MTS to give the message such as the address of the recipient.

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Last update : june 2017