I think these two errors are related.
Exchange ActiveSync AutoDiscover
The Microsoft Connectivity Analyzer can only validate the certificate chain using the Root Certificate Update functionality from Windows Update. Your certificate may not be trusted on Windows if the "Update Root Certificates" feature isn't enabled.
Exchange ActiveSync
The certificate is not trusted on any version of Windows Phone device. Root = CN=Go Daddy Root Certificate Authority - G2, O="GoDaddy.com, Inc.", L=Scottsdale, S=Arizona, C=US
They come from the indicated tests on the Microsoft Test Connectivity site.
I've spoke to GoDaddy and they say the certificates are correct and should cover all Windows devices.
Any suggestions on how to pursue this one?
Bernie