Re: [ietf-smtp] SMTP Reply code 1yz Positive Preliminary reply

John C Klensin <> Thu, 05 March 2020 20:05 UTC

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Date: Thu, 05 Mar 2020 15:05:48 -0500
From: John C Klensin <>
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Subject: Re: [ietf-smtp] SMTP Reply code 1yz Positive Preliminary reply
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I have added a placeholder for this to the list in Appendix G
Section 7 of the working draft.  

FWKW, my personal opinion is that would be a significant change,
outside the scope contemplated for 5321bis.  YMMD and that is,
IMO, a decision that can be made only by the WG when there is
one.  However, if others agree with me, your best course forward
is to write and post an I-D explaining what you think would be
desirable and why, see if you can get it standardized and
implementation reports generated, and then propose it for
inclusion in 5321bis.  


--On Thursday, March 5, 2020 12:56 -0500 Hector Santos
<> wrote:

> On 3/5/2020 11:28 AM, Hector Santos wrote:
>> I used the reply group:
>>     1yz   Positive Preliminary reply
> I had forgotten that RFC5321 had removed this 1yz code.
> All because of the 1yz potentially used as a "preliminary"
> multiple lines "1yz-" response before the final response was
> issued and a possible legacy 821 client that looked only at
> the first response line because it didn't expect multiple
> lines.
> I don't fully recall the discussions. While I would had
> accepted the decision for backward compatibility reasons over
> a decade ago, I am pretty sure I would of been somewhat
> disappointed by the removal of "1yz Positive preliminary
> reply" codes, removing even the possibility of a keep alive
> concept.  Today speeds allow for fast data processing, so even
> today, 5, certainly 10 minutes of idle timeout is outdated and
> probably should be a design taboo today.  If we don't want
> ESMTP 2821 clients to use 1yz, well, maybe for RFC5321bis, we
> can lower the timeouts. I already do for after a successful
> transactions where there is additional 5 minutes wait for a
> new transaction.  I reduced to less than 1 minute to because
> clients from the BIG boys were 99.9% of the time holding up my
> servers and never doing a 2nd MAIL transaction.  So wcSMTP
> will drop clients who chews up available mail service time
> from the server threads.