Exchange 2k3 DNS error

I am in school starting my MCSE….I am setting up a network at my house using a DC and an exchange server..(both running server2k3). the exchange box is running exch2k3 also. I can receive mail fine but outbound mail getrs stuck in the queue and I receive ” remote server did not respond to request” error. I can send and receive to bellsout.net accounts (my isp). Any ideas?