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RE: AD review comments on
At 09:06 AM 10/4/2002 -0700, Dan Wing wrote:
> The timely mechanism satisfies #2. The question is whether that event is
> worth noting.
> In terms of process transitions, it is equivalent to the "return receipt"
> postal function.
It's also the same as a T.30 fax confirmation.
In our effort to make email emulate fax, we have been trying to balance
between two sides of an information dilemma.
Regular DSN provides information about a stage that is earlier than a T.30
confirmation. MDN provides information about an event that is
later. "Timely" is trying to use a middle event.
There is an argument that a T.30 confirmation is actually pretty close to a
regular DSN. It is generated when received by the recipient's "sphere of
There was a strong constituency in the fax community that wanted something
closer to the user than DSN, yet still having hop-by-hop enforcement. MDN
is closer to the user, but does not have the desired enforcement. It also
is generated later than necessary. Hence, Timely uses a middle event.
Besides providing a much better emulation of T.30 confirmation that regular
DSN, I believe that Timely makes email match the postal return receipt
construct. That makes it inherently useful. Postal return receipt is an
extremely important function in the real word. Email needs to have an
equivalent, if email is to be useful for more, and more formal,
> POP has exactly the right name, for the service it provides. It is used
> when picking up mail from a place that is equivalent post office box.
Using POP to indicate receipt extends the current state-of-the-art of
T.30 fax confirmation.
Perhaps. Perhaps not. I think it depends on the precise language one uses
to describe the nature of the feature.
> This event is important in the paper world. Simply knowing that the post
> office has deposited the mail into your mailbox is NOT deemed
So I have been wasting my money with return-receipt-requested?
In fact, return receipt is extremely important for legal verification of
delivery. There is a human that is accountable for the receipt. Timely
does not require human involvement but it does pertain to an action that is
much more directly under control of the recipient.
Some ifax devices decided to use POP, instead of SMTP, to implement their
ifax retrieval function. I have stated for years that this is a faulty
implementation decision, as it requires extending the semantics of
There is a serious, real world constraint, involving connectivity. Some
recipients can only have occasional connectivity. SMTP is not really
viable in that scenario, in spite of 20 years of trying to get it to be
useful for such "polling" environments. POP/IMAP are the only practical
While it would be procedurally better to use SMTP, the choice simply is not
available for some operational situations.
So, we can create facilities that do not match real world constraints,
instead shooting for some sort of ideal. Or we can be practical.
Dave Crocker <mailto:dcrocker@xxxxxxxxxxxxxxx>
Brandenburg InternetWorking <http://www.brandenburg.com>
tel +1.408.246.8253; fax +1.408.850.1850