User mail agent program functions and processes associated with the protocols

I am in the process of learning the details of the Application Layer.  I have come across a question that I am not able to find any information about.  The question reads:
"What function(s) does the local user mail agent program (say, pine) perform and how do they differ from the processes associated with the protocols?"

From what I understand, the functions of pine are:  
? - Help
C - Compose Message
I - Folder Index
L - Folder List
A - Address Book
S - Setup
Q - Quit Program
O - Other Commands
P - Previous Command
N - Next Command
R - RelNotes
K - KBLock

I do not understand what the processes associated with the protocols are.  
CharleneS77Asked:
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DToolshedCommented:
Well, the processes of the protocols would be the commands the client passes to the server, based on what the user does.

The user tells the client to "Check mail", and the client opens communications with the server.
The server says "okay, here I am, ready"
The client says "here is the username of the mailbox I want"
Server says "OK, send the password"
Client responds with the password...etc.
The message is retrieved, and usualy deleted, from the server.
The mail client will store the message, and prepare it for display to the user.

The PROTOCOL part is in the communication with the server. The user doesn't have to sit at a prompt and type "USER joe@domain.com" and "PASS abcxyz" and "STAT" etc...

Those commands are the protocol, and what they do are the processes of the protocol.
USER tell the server the mailbox we want.
LIST gets the list of messages in the mailbox.
RETR starts transferring the message from the server to the client.

See this PDF which show the client/server chatter.
http://www.eventhelix.com/RealtimeMantra/Networking/POP3.pdf
The user never sees this, because it is the protocol level.
The client getting and storing the message and displaying it is the application level.

I hope I haven't confused you more!
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DToolshedCommented:
Basically, it's asking what an email client program is, and how is it different from the protocols that it uses?

Think about what the protocols are used for (issuing commands to, and receiving data from, a server), and what a client is used for (message display, composition, retrieval, etc)

The "functions" of Pine are not the command list, but what it does for the user.

The processes of the protocol are the "functions" it performs, based on the commands sent by the client.

I hope that makes it a little clearer... :)
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CharleneS77Author Commented:
I'm still not clear on how the functions differ from the processes associated with the protocol.

>>>>>"The "functions" of Pine are not the command list, but what it does for the user."
I'm taking this to mean things like:  
1.) Gives the user navigation options
2.) Displays message for the user.  
Is that correct?

>>>>>"The processes of the protocol are the "functions" it performs, based on the commands sent by the client."
This line is confusing.  I'm trying to understand how the functions differ from the processes associated with the protocols.  I know you're not saying the processes are the functions.  Can you rephrase this in a way that might be even easier to understand?

Thank you!
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CharleneS77Author Commented:
That makes much more sense.  Thank you for going into more detail for me.  

The reference you gave is the best one I've seen.  In fact, when I moved out one folder (http://www.eventhelix.com/RealtimeMantra/Networking/), I discoverd a wealth of similar documents.

Thank you again!
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DToolshedCommented:
No problem! Glad to help.
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