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DMARC munging - use X-Original-Sender header
When munging the From address due to DMARC, Google Groups adds the original sender using an X-Original-Sender header.
Mailman adds the original sender to the Reply-To (or Cc in the case where there's a reply to setting in force on the list).
It would be helpful if Mailman could also provide an X-Original-Sender header for the benefit of tools which might need to extract the sender metadata downstream.
I haven't researched exactly what other mailing list tools do, and I'm totally open to suggestions/comments as I only understand this issue from the perspective of trying to parse and extract metadata out of mailing list emails as a downstream consumer.
Edited by Andrew Donnellan