If you use your own server certificates that are not commonly trusted, you have to add the corresponding CA as a trusted root certificate on the clients.
For detailed information about adding trusted root certificates consult the documentation of the corresponding operating system.
You can use the “Certificates” MMC snap-in.
Double-click the CA certificate, add it to the keychain and choose “Always Trust”.
Store the CA certificate in /usr/local/share/ca-certificates/ and execute the following command: sudo dpkg-reconfigure ca-certificates