Target Skills:
Ability to describe in detail a typical message flow through a messaging
system. |
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Detailed Messaging Flow
Now that we know all the necessary components and protocols, we can more
closely examine how a message flows through a messaging system.

Sending Messages
The client sends a message to the messaging server.
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Client does a DNS lookup of its outgoing messaging server.
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Client establishes a TCP/IP connection with the messaging server.
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Client SMTP Delivers the message to the messaging server.
Transferring Messages
The messaging server takes in the message, and transfers it to the appropriate
destination. The server is functioning as a Message Transfer Agent,
or MTA.
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Messaging server SMTP Accepts the message.
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Messaging server does a DNS lookup of the Directory Server.
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Messaging server establishes a TCP/IP connection to the Directory Server.
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Messaging server does an LDAP query to figure out what to do with the message.
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If the recipient is local, the messaging server stores the message.
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If non-local, the messaging server does a DNS lookup of the appropriate
messaging server, establishes a TCP/IP connection, and SMTP delivers the
message to the other server.
Retrieving Messages
The client goes to retrieve the users messages from the messaging server.
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Client does a DNS lookup of its incoming messaging server.
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Client establishes a TCP/IP connection with the messaging server.
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Client establishes a POP3 or IMAP4 connection with the server, and retrieves
the messages.
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