Hi all,some more time has passed, and in the meanwhile an informational IETF draft has been published which discusses the various mitigations to this issue. You can find it here: <https://www.ietf.org/archive/id/draft-levine-dmarc-listugh-01.html>
It does not contain any magical solution, but might be a good starting point for someone wanting to figure out what is happening and eventually working on a fix.
Bye! P.S. my email domain has a DMARC p=reject policy
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