Connecting my domain name from DYNDNS on exchange server

At my house, I have a Windows Server 2008 running with Microsoft Exchange Server. I would like to set DYNDNS so that I could obtain external mails without charges from my Internet Service Provider for a static IP address.
I have a domain name with a local communication network and an account with DYNDNS. I don’t have any problems with the servers, but I would like to connect my domain name from DYNDNS on my exchange server.
How can I do that?
