How do I configure OWA to be accessed from any location?

I’m sure the answer is simple, I just can’t seem to find it.

I configured OWA securely with SSL and Certifications. Within my domain, I and other users can access it on the internet. But from their homes, if they put in the same url, it won’t come up. What am I doing wrong?

I have my Exchange Front End Server in the DMZ zone, and I figured that with using public IP addresses, it would be made accessible.

Can I get someone’s expertise?