Outlook 2003 to Exchange Server 2003 not connecting over VPN

I have exchange server 2003 on a server with 2 controllers. I am able to
ping 1 of the 2 controllers on the external VPN connection, which may control
the connection from the exchange server. Where would I change the controller
settings to only use the single controller as I think this is the problem
that Outlook is encountering. Mail does find the server and resolves to the
name, but Outlook cannot connect to the server.