My client has windows domain setup which has two domain controllers, one is SBS and other is windows 2008r2. We also have exchange 2010 server running on windows 2008r2. We want to get rid of SBS server. But when we shut this server, user stop getting mails. All role right now are moved to windows 2008r2 server and DNS of client is pointing to windows 2008r2 server. Still we have same issue when turn off the SBS server. We want fix this issue before we remove the SBS from network. Please guide me how to fix this issue.