Having an issue with my front end 2007 CAS boxes running RPC Proxy and my backend 2003 Exchange servers (Sp2)(Native Mode). I have two Exchange 2000 SP3 servers as well, but cannot use those as backend servers as they are not supported. All DCs are Windows 2003 SP1 or higher. Read an article that states I need the following keys?? I remember having to enter these keys manually post Exchange 2003 SP1, but after that, all I needed to do was click the front end and backend boxes and the registry keys/ports were auto updated on my frontend servers as well as my DC's. Dont remember having to add the DC in the key as the proxy now does this for you, correct? Also, dont remember the ports 100-5000? Anyway, what do you think about this?. Can I even use Exchange 2007 CAS servers to front end RPC/HTTPS with backend Exch2003 servers? When I click the "Backend Server" check box on the RPC tab, I get a warning that states it cannot find a front end server, however I have my CAS servers setup for Outlook anywhere? Is this even supported? I tried manually editing the registry keys as shown below with no luck Configure ports for the RPC proxy Now that we have the RPC proxy installed, we will need to configure the ports that it uses. To do this, we update a registry key:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\RpcRpcProxy The ValidPorts key will likely already include an entry for ports 100-5000; we need to add a few more. Below is a copy of my key; you will need to change the hostnames and domains to match your own environment. To make this easier to read, I have split the data string into multiple lines. This should be entered as a single line with no spaces after the semicolons.Exchange1:100-5000; Exchange1:6001-6002;Exchange1.internaldomain.local:6001-6002;PDC:6001-6002;PDC.internaldomain.local:6001-6002;mail.externaldomain.com:6001-6002;Exchange1:6004;Exchange1.internaldomain.local;PDC:6004;PDC.internaldomain.local:6004;mail.externaldomain.com:6004;Exchange1:593;Exchange1.internaldomain.local:593;PDC:593;PDC.internaldomain.local:593;mail.externaldomain.com:593; Thanks! NTNEWS