Target Skills:

Ability to describe in detail a typical message flow through a messaging system.

 
     

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.
  1. Client does a DNS lookup of its outgoing messaging server.
  2. Client establishes a TCP/IP connection with the messaging server.
  3. 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.
  1. Messaging server SMTP Accepts the message.
  2. Messaging server does a DNS lookup of the Directory Server.
  3. Messaging server establishes a TCP/IP connection to the Directory Server.
  4. Messaging server does an LDAP query to figure out what to do with the message.
  5. If the recipient is local, the messaging server stores the message.
  6. 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.
  1. Client does a DNS lookup of its incoming messaging server.
  2. Client establishes a TCP/IP connection with the messaging server.
  3. Client establishes a POP3 or IMAP4 connection with the server, and retrieves the messages.

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