Problems with owa/exchange 2007

Hello,

we have problems with connecting to our Exchange Server 2007 per OWA.

Earlier we had a reverse proxy with squid. All works fine. Now we tried to get it working with WebApplicationFirewall.
Our IPhones works without problems with acive-sync.
The problem is connecting from external with a browser to owa. I configured all and now if i try to connect to https://our.domain.de/owa the browser try to connect but i see, that the browser then try to connect to our internal ip from the exchange server?!
The settings in exchange for external domain is correct. But why gives the host (don´t know Astaro or Exchange) the internal ip back to the client?

Example:
--- https://our.domain.com/owa
the browser searches for a while and then get back not found. The address field shows:
--- https://10.172.70.10/owa/auth/logon..../owa/&reason=0

Any suggestions?

Thanks

hwk06