Okay, This has tormented me long enough and I still don't know why it happened.
We have a 2 server network.
Server 1: Windows 2003 Domain Controller, ISA 2006 std, IP: 192.168.1.100, 172.22.6.1
Server 2: Exchange 2003, IP: 172.22.6.2
The way network setup: INTERNET <-----> ISA/DC <-------> INTERNAL NETWORK SWITCH
I published Exchange OWA to public port 80 fine, public name "mail.mydomain.com". The Listener: listens on port 80, FBA with AD authentication
In internal DNS, I set mail.mydomain.com to point to the 192.168.1.100 so that it also displayed the Form based authentication page of Exchange.
Everything works fine, and after yesterday It started reporting problem from firefox "Invalid request (Bad Hostname)" or from IE "HTTP 400 Bad Request".
By logging the request, I can see that the http request never actually got to Exchange Server, it only request to the ISA/DC and stopped there. Details below
Log type: Web Proxy (Forward)
Status: 400 Bad Request
Rule: Allow all
Source: External (184.108.40.206)
Destination: Local Host (192.168.1.100:80)
Request: GET http://192.168.1.100/exchange
Filter information: Req ID: 11f489f0; Compression: client=No, server=No, compress rate=0% decompress rate=0%
From within the company, I can actually type http://Server2/exchange
and access webmail there, but this cannot be published to the internet.
Why is that ? Please assist me