Exchange Server 2003 help!!!!

Im in a Windows environment, i have 3 domain controllers all running Windows 2003 server (one of the DC’s hosts the Global Catalog, and my Exchange 2003 server in my network. Every now and then my Mail server will stop routing mail, meaning Outlook clients cannot connect to it. It seems to me that Active Directory is acting up. All the exchange Services are running when this occurs, and in event viewer i get hundreds of errors, One of them stating that the mail server cannot communicate with our 3 domain controllers.
HELP!!!!!!!!!!!!!!!!!!!! Thanks in advace