I've got a single server with Exchange 2010 installed on Server 2008R2. OWA works OK but remote Outlook 2007 clients can't connect.
This all worked OK on the same machine and network and router when I had Exchange 2007 running on Server 2003. The only way I can get remote Outlook clients to connect to the Exchange server is enable the DMZ feature on my router. I don't think this is a recommend action.
I checked www.testexchangeconnectivity.com
and ran the Outlook Anywhere (RPC over HTTP) test and it failed with the error "Http Authentication Test failed. A Web Exception occurred because an HTTP 404 - NotFound response was received from IIS7"
I don't know if I have an Outlook Anywhere issue or another problem.