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Re: [ietf-smtp] SMTP status codes 251 and 551

Alessandro Vesely <vesely@tana.it> Tue, 11 February 2020 09:52 UTC

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From: Alessandro Vesely <vesely@tana.it>
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Date: Tue, 11 Feb 2020 10:52:25 +0100
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Subject: Re: [ietf-smtp] SMTP status codes 251 and 551
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On Tue 11/Feb/2020 03:45:58 +0100 John Levine wrote:
> In article <CAO=DXp-j4OFwiPqLHvNzQ+dL+CNE0t58AZ33pxaBkBBWce2+NA@mail.gmail.com>,
> George Schlossnagle  <george@sparkpost.com> wrote:
>>We see a good bit of email here and the number of 551s that seem to
>>indicate forwarding is being suggested is incredibly tiny.  I could run
>>some stats if you like, but call it < 0.0002% over the past year's bounces.
> 
> Thanks.  Do you see any 251 at all?


251's cannot be seen, except in the mail log.  While "551 send to <x>" is
manually actionable by the author who receives the bounce, 251 is not, unless
someone enables positive delivery notification.

FWIW, in my tiny log files I found a few improper replies like the following,
in the period September-December 2014:

    551 5.0.0 This message was classified as spam

and no 251 at all.

Using Courier-MTA, I'd have to devise a new add-on in order to issue these
responses using configured forward addresses.  Do Sendmail or Postfix provide
for email address portability?


Best
Ale
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