I have DKIM and SPF configured, together with a DMARC policy, and most emails seem to be passing with no problem. I currently have my policy set to 10% quarantine. However, when I view the Policy planner, it says “Publish a stronger policy” but has the following Note: “You have some forwarding volume that is not fully dmarc compliant. A more aggressive policy may prevent delivery of forwarded emails that do not pass DMARC (by preserving DKIM keys).”
Here is a screen shot of the Detail Viewer, filtered with “Show impact of policy”.
There isn’t anything you can do in that situation. Recipients with poorly implemented email routing is a “them” problem, not a “you” problem. They may be aware that their implementation breaks authentication and ignore it accordingly. They may wonder why they don’t see some of their email. Either way, you can’t fix anything that is broken by their setup.