Re: [Exim] Reaction to rude 554 greeting

At 13:09 -0500 2003/03/18, Greg A. Woods wrote:
>[ On Tuesday, March 18, 2003 at 11:05:37 (-0500), Eric Kuzniar wrote: ]
>> Subject: Re: [Exim] Reaction to rude 554 greeting
>>
>> But you never had the situation where one of the bosses was
>> decommisioned but that information just didn't propagate to you yet.
>
>No, a "de-commissioned" SMTP server will return TCP RST packets to
>connection attempts on port 25.
>
>Any idiot configuring a de-commissioned or "out-of-service" SMTP server
>to return any 5xx response gets what he or she deserves -- no e-mail.

Sorry, but Eric is the only person here having shown lack of
preconcepts. You do not like 2821, fine, but keep your opinions as
yours and do not try to sell them as the RFC truth. You have not
understood 2821, fine, that's your problem. I admit that they could
have put it more clearly, but it seems to me that the interpretation
and the course of action that I suggested is the most reasonable.

Why did they introduce a 554 on connect? Well, perhaps because DNS is
not part of SMTP and also because DNS has, by nature, updating
delays. Can be done with a firewall? Maybe, but that is not part of
SMTP, again.

> > Interpret 554 to be something along the lines of that decommisioned boss
>> saying I cannot answer that for you.
>
>No, do not do that because doing so would be wrong. Any 5xx is an
>indication of a _permanent_ delivery failure and _MUST_ be treated as
>such.

well, then you should go and look how 5yz are treated in 2821 and 821
and see that in "permanent error condition" the "permanent" is indeed
quoted, as it can indicate condition that may be corrected. I admit
that the RFC does not explicitly allow for automatic corrections,
but... you should go and see how MXes should be used, per RFC 2821,
and see that you must try MX until a delivery attempt succeeds. And
what "delivery attempt succeeds" means? It does not clearly mean "try
until a host accepts the message", but it means try until you succeed
in attemtping a delivery, that is until you connect to an SMTP server
that is also an MX for this domain.

Now, you have been sent to buy some nails, and directed to a hardware
shop at number 10 in the High Street (preferably) or to another
hardware shop at another address. You go to the first shop and ask
"got any nails?"; no, says the owner, this is a butcher. What do you
do? Go back home or try the next one?
You try the next one (that might tell you that they do not sell nails
anymore at hardware shops, but that's a 550, or a 450 if they run out
of stock).
Then you go back home with the nails (or not) and tell whoever sent
you that the first shop is a butcher (this is the warning message to
postmaster that I suggested).

(dad always told me not to talk to engineers...)

Giuliano