Outlook disconnects from MS Exchange server 2003 over night

I have a situation in which MS Outlook 2003 from 3 client PC’s gets disconnected from the Exchange server over night. All the client mapping drives to the data volumes on the server work and information can be retrieve from it, but the email and calendar portion of the server stops responding. The client needs to restart the server every other day to reestablish communications.

Any ideas guys?