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.