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We provide cmail delivery for external clients from several different domains. We rewrite the envelope sender (AKA: "SMTP MAIL FROM","Return-Path" ) using a form of VERP. Thus we receive all the late bounces and have responsibility to forward them on to the original envelope sender.

These NDRs have no domain in the envelope sender so SPF does not apply, but it seems that these messages could fall foul of DMARC when we attempt to re-deliver them.

On these received NDRs should we be re-writing the From: email header to postmaster@ourdomain.tld or should we leave it as-is?

Jasen
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RFC5322 3.6.6

Note: Reintroducing a message into the transport system and using resent fields is a different operation from "forwarding". "Forwarding" has two meanings: One [...]. Forwarding may also mean that a mail transport program gets a message and forwards it on to a different destination for final delivery. Resent header fields are not intended for use with either type of forwarding.

This would be forwarding (sense 2) so "NO, don't do that"

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Jasen
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