Sharepoint OWA cannot be access from external network

Hi,

I have problem with OWA sharepoint 2013. The problem is that i cannot access owa (edit or preview documents from different trusted domain). OWA service works from internal domain.

let's say I have single sharepoint server (SPS-SVR) with an owa server (OWA-SVR)

the URL name for external is https://spsweb, I already set the DNS in external network but the browser keep gives error saying that "OWA-SVR can't be found". I though it's because the SSL connection, but if i change back public URL to http, the OWA service also doesn't work from external network.

Is someone understand this problem? anyone had same problem with me?

Thanks