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DATA, 221, and close (was: Re: RFC2821bis-01 Issue 8 number of message transactions per connection ?)

2007-03-29 08:59:36



--On Thursday, 29 March, 2007 08:29 -0700 Bart Schaefer
<barton(_dot_)schaefer(_at_)gmail(_dot_)com> wrote:


On 3/29/07, Tony Hansen <tony(_at_)att(_dot_)com> wrote:

<implementor's hat>

  Side note: An implementation is free to respond with 4xx
  (e.g., 421, 451 or 452) to the MAIL FROM whenever it wants
to shut down the connection. And some implementations *do*
choose to do so because of local policy decisions.

</implementor's hat>

Recently I've encountered servers that respond with 221 rather
than
250 at the end of the DATA phase (after <CRLF>.<CRLF>) and then
immediately close the connection.  (This may not be a
recently-developed practice, but I noticed it for the first
time last
week in an SMTP client log when tracking down a delivery
problem.)

There is at least one well-known server that behaves in this
general way (perhaps not this specifically).  It is generally
believed to be non-comformant in many other ways as well.

It would appear this is meant as an indication that the server
intends
to accept exactly one message and doesn't care to wait for a
QUIT.

The developer of that server has argued that he should not need
to wait for a QUIT and that, when the same software is operating
as a client, he should, at most, send a QUIT and then close
without waiting for a response.
 
I'm not sure what, if anything, could be put into the document
about
this.  Perhaps guidance as to how clients should react when
the server
wanders off-protocol?  In the case I was investigating the
client
treated the situation as a 4yz and retried the message later,
leading
to a lot of copies being delivered and (fortunately just one)
irate recipient.

That would strike me as client behavior within the intent of the
protocol.  And, no, I don't have any idea how to write up
suggestions about how clients should deal with misbehaving /
non-conforming servers without getting into a rather large
rathole.  I think there might well be a place for an "SMTP
operations in  the face of stress, stupidity, well-intentioned
by out-of-spec spam solutions, and deliberate misbehavior", but
I don't think it should be part of 2821bis.

(I've also seen 221-and-close responses to EHLO, which seems
entirely bizarre.)

yeah.  Presumably, it would mean "I'm closing now, but I thought
your EHLO command was ok, so keep trying".  And I can't imagine
why one would want to deliver that message.

I have not assigned an issue number to this one.  If someone
wants to state it as an issue or request for action, please do
so.

    john

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