A SME server that is NOT configured to use "Internet DNS servers" (in server-manager::Configuration::Domains::Modify) will create DNS entries for ftp.xyz.com, mail.xyz.com, <servername>.xyz.com, proxy.xyz.com, wpad.xyz.com and
www.xyz.com.
These names are ONLY available to your internal network.
Hosts on the Internet outside your local network will only be able to lookup the host names you have created at your DNS hosting provider.
The internal host names will not exist unless the specific domain in question is configured to "Resolve locally" (in server-manager::Configuration::Domains::Modify)