Can't access Exchange 2000 from Outlook over the Internet

[Ed Register]

We are having a problem getting to our Exchange 2000
server from Outlook over the Internet. The message we get
is "Your Microsoft Exchange Server is Unavaliable".

We can access Exchange 2000 from the Internet using
Outlook WebMail. We are using the same DNS name in both
cases.

We can access Exchange 2000 from our INTERNAL network
using Outlook or WebMail.

Anyone with any ideas would be greatly appreciated.

I'm wondering if their is an RPC issue with the LAN
adapter on the Internet side of our Exchange server??

Thanks in advance,
Ed