We have aresource forest with linked mailboxes. Planning to collapse the resource forest and install Exchange in the user forest. Resource forest is 2010 sp1 and the user forest will be installed with 2010 sp1 as well. Export-autodiscoverconfig was run with resource forest setup. What will happen when the 1st CAS server is installed in user forest? The SCP will be created and will outlook use the Resource forest SCP or the SCP created by new exchange install.

set the scp on the new CAS servers in user forest to https://autodiscover.domain.com/autodiscover.xml This way the users are still routed to resource forest as the DNS points to it. Once the users are migrated to Exchange in user forest then flip the records.