I am migrating our Exchange environment to Exchange 2010. We are using ISA 200 as our firewall. I set the firewall rules to point at the new server and created rules for our legacy server. I then changed DNS entries to point the MX record at the new exchange box. Internally, I can access the mail website and get the Exchange 2010 signon screen. I can signon and access my mailbox which still resides on 2003. Externally, when I access the mail website, I'm still being presented with the 2003 signon screen. If I signon, I get the 2010 signon screen. Signing on a second time fails. I've tried deleting the cache on ISA 2006 to no avail. I'm reasonably certain there is a cache involved somewhere because I get a signon screen for 2003 when both exchange servers are shut down. What am I missing?

The 2003 login screen is actually coming from ISA. If you are using ISA to do the authentication you should change the settings on the Exchange 2010 server to remove forms based authentication - in much the same way that you would have done with Exchange 2003. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.