Re: [Asrg] reject and DSN, was What are the IPs

John Levine <johnl@taugh.com> Thu, 02 July 2009 13:54 UTC

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Date: 2 Jul 2009 13:54:09 -0000
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From: John Levine <johnl@taugh.com>
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Subject: Re: [Asrg] reject and DSN, was What are the IPs
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>> Why should it do anything different from what it does the other 95% of
>> the time?  SPF is far from universal, and a whole lot of SPF lookups
>> end up saying "maybe".
>
>You've avoided the question. SPF and DKIM are both growing quite rapidly. 
>Some day, you'll get a definite answer for most of your mail. Or, perhaps 
>it'll be some other sender domain authentication technology.

That may be so at some time in the distant future, but for the
forseeable future there will always be a signficant number of maybes.

>So, why should one NOT send a DSN when the domain is authenticated?

Because rejects work better, and DSNs are a second rate substitute
when the recpient system can't tell during the SMTP session that the
delivery will fail.

You appear to be under the impression that a sender would obtain and
use valuable information from a DSN that can't be sent in a rejection,
which is completely contrary to my experience.  I don't spend an
enormous amount of time reading DSNs, but my mailing list software
does and all it really wants to know is the address that bounced,
which rejections reliably provide.  DSNs often give no hint what
address the bouncing message was sent to.  That's why we have to use
kludges like VERP.

R's,
John