Mailgun Config with Fastmail Domain

Hi all,

My Ghost site runs on a Digital Ocean droplet and my domain is managed by Fastmail, mainly because domain hosting comes with the service.

But I’m having a bear of a time getting Mailgun to be configured correctly for everything except my DMARC record:

Before I spend a ton of time troubleshooting this, just curious if any self-hosters out there are running their domain via Fastmail so we can try to talk this out!

Thanks,
Craig