On May 24, 2007, at 8:35 AM, Henning Brauer wrote:
> * Bob Beck  [2007-05-24 08:22]:

quoted text
>>> rfc 2821 specifically forbids this behaviour.

>>>

>>> 

>>> The DATA command can fail at only two points in the protocol

>>> exchange:

>>>

>>>    -  If there was no MAIL, or no RCPT, command, or all such

>>> commands

>>>       were rejected, the server MAY return a "command out of

>>> sequence"

>>>       (503) or "no valid recipients" (554) reply in response to

>>> the DATA

>>>       command.  If one of those replies (or any other 5yz reply) is

>>>       received, the client MUST NOT send the message data; more

>>>       generally, message data MUST NOT be sent unless a 354 reply is

>>>       received.

>>>

>>>    -  If the verb is initially accepted and the 354 reply issued,

>>> the

>>>       DATA command should fail only if the mail transaction was

>>>       incomplete (for example, no recipients), or if resources were

>>>       unavailable (including, of course, the server unexpectedly

>>>       becoming unavailable), or if the server determines that the

>>>       message should be rejected for policy or other reasons.

>>

>> and that paragraph says right there, the server can decide it doesn't

>> have the resources to deal with it. no problem.  The RFC does not

>> forbid it

>

> yes, but not in response to the DATA command (what I was talking

> about)

> but after.

I agree with you Henning that per that paragraph a 4xy should not be

sent as a reply to the data command itself.  Instead a 4xy should

only be sent after a 354 has been sent and all the data received.

Which of course would undermine a lot of the benefit of spamd.  I

think one of the points is to reject the mail before the data is sent

down the pipe, allowing the data wastes the receivers bandwidth.
I went looking in other places within these two RFCs for indications

that a 4xy is legal in response to the DATA command.  I think I've

found points in both RFCs that make it legal to send a 4xy in response.
 From 821
4.3.  SEQUENCING OF COMMANDS AND REPLIES
.

.

.
     DATA

                I: 354 -> data -> S: 250

                                  F: 552, 554, 451, 452

                F: 451, 554

                E: 500, 501, 503, 421
 From 2821
4.3.2 Command-Reply Sequences
.

.

.
     DATA

       I: 354 -> data -> S: 250

                         E: 552, 554, 451, 452

       E: 451, 554, 503
Thus I think spamd is within the RFCs when it issues a 451 in

response to the data command.
>

quoted text
>> and 821 (which ain't dead yet) allows explicitly in the state

>> transactions.

>> 2821 is simply vague.

>

> well, 2821 is somewhat vague, 821 is kinda the definition of vague :)

Yup.
-Chad