kyle-qmail at memoryhole
Nov 2, 2009, 8:54 AM
Post #7 of 7
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On Monday, November 2 at 05:06 AM, quoth John Levine:
>> It depends on when the error is given. For example, if a 554 error is
>> given upon connection, what does it mean?
>
> According to RFC 5321 it means "No SMTP service here", or to put it
> more concisely, FOAD. Whatever you thought you were going to send,
> forget it, treat it as a failure and don't try again.
RFC 5321 is a draft barely a year old, so you'll forgive me for not
being intimately familiar with its contents (heck, DKIM is more
venerable). :)
The behavior that I was describing is often used by misguided
administrators following a policy whereby their most-preferable
(lowest-ranked) MX record is a fake "SMTP" server that responds to all
commands with a 554 error. The idea (and, as far as I can see, RFC
5321 merely codifies this idea) is that the sender should then
re-attempt the delivery by contacting the next-most-preferable MX. It
should not cause a termination of the message you were attempting to
deliver, but should instead be treated as if the connection could not
be established. (You'd think that simply refusing the connection would
be easier and more efficient, but...)
Section 4.2.2 says:
554 Transaction failed (or, in the case of a connection-opening
response, "No SMTP service here")
Now, given that a greeting 554 is technically (according to this RFC)
part of the SMTP protocol, that's kinda like saying "I do not speak
English". But it's explicitly *not* saying FOAD, and as far as I can
see should have the exact same effect as simply refusing the
connection.
But perhaps I'm misreading this new RFC. Where does it say that the
error should be treated as a permanent termination of any and all
messages you were intending to deliver?
>> answer is: no, of course not. Just because it's a 5xx error doesn't
>> mean that the *message* was permanently rejected.
>
> Well, yeah, actually, it does. Typically it means that the host
> has blacklisted you and doesn't want your mail.
Really? In my experience, it virtually always means the admin of the
recipient domain is following a (broken) modified "nolisting"
anti-spam policy.
>> Here's another example: when I send the SMTP command "QUIT", the
>> server I'm connected to is SUPPOSED to respond with a 221 code. By
>> that point it's already claimed to have successfully accepted all
>> messages that I've sent. But if the server respond with a 554 code
>> instead, what does THAT mean?
>
> That's broken, QUIT can only return 221. Treat it any way you want.
I agree that it's broken; but my point is that recipient servers can
behave badly in a variety of ways, and in particular can generate
bogus errors at a variety of points that would cause qmail to log an
error message that does not indicate that the message delivery
actually failed (either permanently or temporarily).
~Kyle
- --
Coffee is the common man's gold, and like gold, it brings to every
person the feeling of luxury and nobility.
-- Sheik Abd-al-Kadir
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