What is the url for my OWA?

I setup OWA on my Small Business Server. I want to use it to access my email from any internet connection when I’m not in the office. I’ve tested OWA at the server using http://localhost/exchange and it works perfectly. I am also hosting my website on the SBS, and Exchange is running on the same server. There is a unix firewall between the internet and the server. What I don’t know is what URL should I use to access OWA when I’m not in the office? Thank you.