Treat dkim-signed mails from our own domain from external relayhost to exchange online, as internal

Hi Folks,

we use some 3rd-party web-applications that send mails to exchange online via a relay-service. These mails carry a valid dkim-signature for our primary domain (d=...). Sender address is our accepted (primary) maildomain.

Exchange Online marks these mails as outside of the organisation, as they are neither authenticated via sending-IP, nor certificate. As the relay-service is a shared service, we do not want to whitelist the ip or ssl-cert as others use this system as well.

Is there a way to use the dkim-signature to treat this mails as internal?

Thank you.

Siegmar