Ok I will first explain the network topology.
I have 2 exchange 2003 servers on the same network. One exchange server is running SBS2003 and the other exchange server is running Server Standard 2003R2 with Exchange 2003 standard installed. The SBS2003 server host the primary domain and is running, active directory, dns, and dhcp. The second server host a sub domain and is running exchange, active directory, and dns. I have clients that have email accounts on both servers. Their computers are joined to the first domain. I have configured Outlook 2010 to connect to both exchange servers.
For some reason when trying to send emails using outlook 2010 from the sub domain email account to a user that has a primary domain account the server responds saying "The message could not be delivered because the recipient’s destination email system is unknown or invalid". Now if said user logs into their email using owa it works fine.
Any help will be greatly appreciated thank you for your time.