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Re: Email System Model

2009-05-17 10:43:33

In my view, you have an over simplification and Crocker's doc is attempt to model a more complex integrated world. Its one view abeit one that attempts to prescribe a model based on STDs and RFCs. I think it could of been done in a more readable fashion, like a Requirements/Optional Grid to start work ala RFC 1153

I do think, in my opinion, your first illustration is pretty fundamental and much easier to understand, grasp without reading the context. IMO, Dave's doc is too overwhelming for MOST people to read - totally only useful for highly IETF trained geeks.


Hector Santos

David MacQuigg wrote:

I'm splitting this off as a separate topic, so we don't distract from the discussion on email-arch. In this thread, I welcome discussion of the validity of the model at

This model is focused on what happens at the administrative level in one transit through the Mail Handling System, but it can easily extend to systems involving multiple transits. To model the situation Austin describes, I would put two "one-transit" models in series.

Author ==> MSA/Transmitter --> / --> Receiver/MDA ==> Mediator

Mediator ==> MSA/Transmitter --> / --> Receiver/MDA ==> Author

The Mediator is a separate user-level Actor, even if it is automated. The final Recipient is the original Author.

I'm not sure if I fully understand Austin's concern, so I don't know if more elaboration of the model will help. A model is only as good as its ability to clarify real-world systems, helping with questions like "What happens if ...", or "How should I ...".

Best Regards,
David MacQuigg

Cheney, Austin wrote:
David MacQuigg,

One difference that I see is an inferred conceptual implementation that
is explicitly not presumed in your model, while being completely
unmentioned or challenged in David Crocker's models.  This inferred
conceptual implementation is that a mail server is a mediator in the
communication process between author and intended recipient, but a mail
server can become an participant if were acting as an application

Let me demonstrate this in the model of software as a service.  Suppose
I were communicating with a known destination, such as a retailer, who
receives and replies to mail as an automated application system.  At the
same time another content application system is installed on the local
mail server of this intended recipient that is capable of intercepting
communications, making decisions upon those communication, and sending
automated responses that beg further communication from the initial
author.  In this model application programming and scripting can be
running in response to human supplied communications from the
originating author, while those same applications can also be relaying
data relevant only to the distant end to the intended recipient for
status responses and session content details.

In that model the mail server of the distant end transforms from a
mediator to an intermediate responding agent.  Such a model could allow
things such as cloud computing or ecommerce.  It is not practiced by
anybody, because a definable characteristic that is uniformly described
and universally understood would have to exist in the content to provide
such a hook for application engagement.

So, in summary, a mail transfer agent MUST NOT be presumed to be
separate from a designated point of intended receipt.  Crocker's models
do not mention or challenge this concept, but your model does imply such
a challenge.

Austin Cheney

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