Re: [dmarc-ietf] Some Proposed Language for a New pct Tag Defintion

["Murray S. Kucherawy" <[e-mail]>]

On Thu, Aug 5, 2021 at 4:22 AM Douglas Foster <
[e-mail]> wrote:

> PCT could work IF evaluators are willing and able to send a Temporary
> Error result (probably 451), instead of a permanent error, when
> - a DMARC verification fails,
> - the message is not unconditionally blocked or accepted on other
> criteria, and
> - the sender's PCT is between 1 and 99.
> The result should include an extended status code in the 4.7.2x range.
>
> This approach assumes that the temporary error status will cause the
> sender to retry multiple times over an extended period.
>

It should, since that's what the standard says ought to happen.  But then,
as was observed elsewhere in this thread, not all clients behave that way.

Based on observed configurations, this probably works out to at least 10
> attempts.  In most cases, the PCT formula will cause the message to be
> accepted after a delay, which is a result equivalent to PCT=0.
>

We usually use 4yz SMTP reply codes to mean there's some transient
condition preventing delivery; a later retry may yield a different result.
Random chance seems an awkward thing to shoe-horn into the notion of
"transient condition".

I think this could also DMARC skew statistics, as now any given message
could result in multiple distinct delivery attempts over a period usually
measured in days.  Care would have to be taken to identify and aggregate
the ones representing the same message.

-MSK