Re: [dmarc-ietf] Report bombing is a prolem, Forensic report loops are not

John R Levine <johnl@taugh.com> Wed, 03 February 2021 16:55 UTC

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Date: 3 Feb 2021 11:55:45 -0500
Message-ID: <a869fa7-bff9-dbd7-3b77-dbe8f12f3653@taugh.com>
From: "John R Levine" <johnl@taugh.com>
To: "Alessandro Vesely" <vesely@tana.it>, dmarc@ietf.org
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Subject: Re: [dmarc-ietf] Report bombing is a prolem, Forensic report loops are not
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On Tue, 2 Feb 2021, Alessandro Vesely wrote:
>                          Whatever mechanisms are used, servers MUST
>   contain provisions for detecting and stopping trivial loops.

I can tell you from bitter experience that rate limiting is the *ONLY* 
reliable way to stop trivial loops.  Whatever else you try, something will 
eventually change or delete the thing you try to use to recognize loops.

As a concrete example, I get a lot of failure reports from 
antispamcloud.com which are not multipart/report and which software would 
not recognize as a failure report.  Nonetheless, if they got into a 
reporting loop, it would be annoying, and rate limiting would stop them.

> Mailbombing in general is not a loop.  Two report generators reporting each 
> other's failure to authenticate a failure report /is/ a loop.

Sometimes mailbombing is a loop, sometimes it isn't.  If the loop is so 
slow that it doesn't trigger rate limits, it's not likely to be a 
practical problem.

Regards,
John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly