Pete,
An elaboration on the second diagram occurs to me, with some
clarification of the terminology:
2. How do we model the components and downstream interactions of srv2 and pc2:
|
+---MTA----+
| |
| messages |
| |
+----------+
|
+--<srv1>--+
| |
| messages |
| |
+----------+
|
+--<pc1>---+
| |
| messages |
| |
+----------+
Messages are retained on pc1 and not on srv1.
The difference between "moving" a message versus copying, of course, is
that a message is retained in its original location when there is
copying, and not retained with there is moving. Hence, MTA-MTA
transfers involve moving.
So, the difference between the diagram that showed the pc as having no
<messages> versus the one that shows it as having them is about
long-term retention after a move. When PC1 is shown with no <messages>
it means that it does take over responsibility for the message.
And the reason for elaborating the MTA depiction is to raise the
question about the distinction between the MTA and srv1. When pc1 takes
over responsibility for a message, as a result of a moving it to the
pc1, what is the difference between MTA's holding messages and srv1's
holding messages? Both are used for queuing, and both hand off
responsibility to the next machine in the sequence.
d/
--
Dave Crocker <mailto:dcrocker(_at_)brandenburg(_dot_)com>
Brandenburg InternetWorking <http://www.brandenburg.com>
Sunnyvale, CA USA <tel:+1.408.246.8253>, <fax:+1.866.358.5301>