Re: Email System Model
These are my own technical writing methods and for this type of
subject, this would be some of my initial inclinations as a first
approach using a system engineering (component, blackbox, functional
models, etc.) standpoint.
Very important to begin with a legend of well known
acronyms representing components of the network.
MTA, MUA (UA), MTA,MSA, MDA, etc, I would probably add MLS for
Mail List Server, a very important part of the infrastructure,
and MGS (Mail Gateway Server), etc.
- Message Structure
I would do a basic overview of the fundamental common message
structure in ALL networks, starting with the basic idea that
every "Communication" system and with mail, five basic elements:
Date: (Creation Date)
You can then introduce the extensions and variations to be
discuss in more detail elsewhere.
- Transport Structure
I would begin to talk how Messages are wrapped with Transport
Networking layers, envelope idea, etc. which can lead to
the next subject.
- Offline, Online, Store and Forward
I would also touch based with these ideas as is related to
topologies and how data is created, sent and delivered. I
would break this down to three parts:
- Message Creation
- Message Transfer
- Message Delivery
- Topologies or Functional Models
I would then probably talk about topology and the various
common ones, including maybe the history from centralization,
distributed, to maybe even back to centralization. I would
start with a general overview (like what you have),
UA --> [ MODELS ] --> UA
and then show expands of the various models, from simple routes
to more interfacing domain complex.
- List of technologies
Here I would begin to talk about the ideas that extend or
help the process. You can list the IETF protocols here and begin
to show these how they fit into the topologies and mail flow.
And so on, the exact order above could change of course.
If this may help, since you are targeting students, one of my first
intros to the growing communications market, was a first edition book
I read long ago that covered the technologies of the day (including
BBSes) and the directions might be useful:
Thomas C Bartee
First Edition, 1986
Its chapter on Electronic Mail System architectures is still valid
today, there are also discussions on email security still valid today
(i.e. the issue of anonymous senders and the forging potential).
It might worth your time to see if there are newer editions or grab
the old one and see how he approached the subject.
David MacQuigg wrote:
Hector Santos wrote:
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
Standard textbook models are much simpler than what I am proposing. The
most popular book (Peterson & Davie, 4th ed.) has just a sequence of
"gateways", and no good explanation as to why so many are needed. The
two reasons given are 1) The recipient does not want to disclose the
actual host on which he reads his email, and 2) The recipient's machine
may not always be running, and a "gateway" can hold the message until it
is ready to be delivered.
What I'm looking for is a model that is almost as simple, but a better
foundation to understanding real systems. We have maybe half a week in
a 3-unit class on Computer Networks, so we clearly can't cover all the
details in email-arch.
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.
My primary goal is optimizing the model for students. A secondary goal
is conformity with standards. There is always a tradeoff. If we
simplify too much, students will not learn how real systems work. If we
add too much detail, or use jargon instead of plain English, students
will learn less of the fundamentals that are needed long after passing a
I'm looking for constructive criticism. If you believe the model is
oversimplified, give me an example of an important system that the model
should cover. If you think you can improve on the terminology, give me
some specific alternatives.
The model is still work-in-progress, but the most complete description
is at http://open-mail.org/MHSmodels.html
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