We're using Axigen mail server, and in that for the local webadmin and webmail IP's we are using a Cloudflare Client Certificate for SSL. When importing the certificate and private key into Axigen, it shows "No CA" as it cannot identify the Certificate Authority which I guess is why I'm running into this issue.
When attempting to access the page you get the error net::ERR_CERT_AUTHORITY_INVALID
Yeah Client Certificates are for MTLS. Seems like the server requires a public validate SSL certificate. You could make a DNS record that points to the local IP and use that for Let’S Encrypt.
We might consider doing that when we implement an internal DNS, I was just curious if it was possible to get the .ca file which seems to be to identify the Certificate Authority.