Welcome back, Michael.
[forwarding without changing the envelope From]
In a hypothetical world, all email is signed with DKIM, and forwarders
don't break DKIM signatures, so that DMARC will accept the messages.
The Postfix mailing list still relies on this but it is becoming a
curiosity.
In a more pragmatic world, forwarders replace the envelope from and
update the header From address to align it with the envelope from,
and maybe add a header with the original DMARC result. This envelope
sender change breaks the reverse channel for delivery status
notifications.
Some providers implement SRS but that is relatively rare.
Basically, anything that requires two-way email forwarding is dead.
Wietse
