After the Partner Exchange Server has a maintenance reboot, the Cisco Unity Service does not start.On the Cisco Unity server, there are errors related to services and Digital Off-Hook (DOH) starts to show up in the Application Event Log.
These errors are mostly due to a Messaging Application Programming Interface (MAPI) login failure. If in the Active Directory Users and Computers option is checked for the location of Unity_ account, it shows up on a store that is offline.
In order to resolve this issue, delete the Unity_account from the Active Directory shown on the store which is offline. Run through the Message Store Configuration Account and create a new one on a functional store.
For more information about how to change the Partner Exchange Server and troubleshoot issues, refer to these documents: