There is a problem with the proxy server's security certificate.
The name on the security certificate is invalid or does not match the name of the target site mail.domain.com
Outlook is unable to connect to the proxy server. (Error Code 0)
- The Root certificate is installed correctly on the server with the correct thumbprint.
- The intermediate certificate is installed correctly on the server with the correct thumbprint.
- Awildcard certificate is installed on the server with private key and the certificate chain is healthy.
- The certificate is valid expiry date and has a valid subject name.
- All names on the virtual directories for Exchange match a valid name trusted by the wildcard certificate.
"RPC/HTTP Connection Flags"
This is located under User Configuration --> Administrative Templates --> Microsoft Office 2013 --> Account Settings --> Exchange
Provided you have the Exchange 2013 ADMX installed in the Group Policy Central Store.