I need help with a couple of clients that we are hosting data for. Two of the clients have their own Exchange server (one 2007/ one 2003). Since moving them both to the datacenter, the two companies cannot email each other. They can email most everyone else, but not each other. I also cannot ping from one mail server to another unless I put an entry in the host file of each machine. I think, therefore, it's a DNS issue. I have one Cisco PIX firewall/router. Therefore, each client I have setup right now on the same IP range and I'm wondering if that is part of my problem. For example, client A uses IP's of 192.x.x.20 to .29 and client B uses .70 to .79. Could that be my issue? Do I need to setup something on each company's DNS server to see the other? I have a managed DELL switch with VLAN's that I am waiting for my IT guy to install to separate the networks. Is that the problem?