Question : Exchange server email unavailable until reboot of Domain Controller

Our Exchange server email becomes unavailable about every 2 weeks, when I reboot the DC email becomes available. I've tried to restart services on the Exchange server (MTA Stacks, Information Store) and I can't restart the services when this happens, the only way to get email to start working again is to reboot the Domain Controller and I don't know what is causing the problem. I look in the logs and don't see anything that may be causing the problem. Does anyone know what might be causing this and what can be done to prevent this?

Server 2003, Exchange 2003, XP Pro network environment.

Answer : Exchange server email unavailable until reboot of Domain Controller

Low disk space (on DC, or exch).
Is it always every 2 weeks?
Is your DNS running on the domain controller?  Try restarting just DNS.  Hell, try restarting each service on the DC and see if any make mail flow.