Re: [ietf-smtp] DSNs

Viktor Dukhovni <ietf-dane@dukhovni.org> Sat, 18 April 2020 19:42 UTC

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From: Viktor Dukhovni <ietf-dane@dukhovni.org>
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Date: Sat, 18 Apr 2020 15:41:59 -0400
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Subject: Re: [ietf-smtp] DSNs
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> On Apr 10, 2020, at 5:04 AM, Claus Assmann <ietf-smtp@esmtp.org> wrote:
> 
> On Thu, Apr 09, 2020, John R Levine wrote:
> 
>> Oh, RFC 3461.  Agreed, it's basically an SMTP level web bug.  Nobody
>> implements that.
> 
> sendmail implemented it too (more than 20 years ago?). I guess it
> should read "nobody enables/uses it"?

And likewise Postfix also implements RFC3461.  It is on by default.
I turn it off on inbound edge systems, and ignore remote "DSN" on
outbound edge systems.  That way, any DSNs are sent within either my
or the remote ADMD, but not across ADMD boundaries.

Bounces are of course delivered in DSN (RFC3462) form regardless of
whether the DSN ESMTP extension is enabled or disabled.  That is,
when DSN is disabled messages sensibly default to "NOTIFY=FAILURE".

A side-effect of entirely disabling DSN inbound is that NOTIFY=NEVER
is no longer honoured, even if supported earlier along the forward
path, when any message I accept from outside ultimately bounces inside
my system.  This is rare enough to not be an issue.  Arguably it should
be possible to advertise just "NOTIFY=NEVER", but there's no mechanism
for that.  Simpler to just use an empty return path.

-- 
	Viktor.