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