Generic Email Forwarder: Servers that 'Forward' email and preserve DKIM
DMARC-capable receivers can identify sources of email and flag them as a "forwarder" if the receiver believes the source of email is forwarding email. In this case, the DMARC-capable receiver does not wish to apply DMARC policy against the email source. This local policy decision is specific to the DMARC-capable receiver. The preservation of DKIM makes categorization as a "forwarder" fairly easy.
No action can be taken unless the DMARC-capable receiver appears to be miscategorizing an illegitimate source. In this case, contact the DMARC-receiver directly with evidence of illegitimacy.
When deploying DMARC, domain owners often find that email can flow through forwarders before arriving at a final destination.
Domain owners then wonder if the forwarder is capable of interoperating with DMARC.
This directory contains information on the capabilities of various email forwarders.