SYMPTOM:
When trying to send emails using Distribution Services in Strategy 9.x, many delivery failed emails are sent to the administrator. The following error can be seen in the DSSError.log
Distribution Service: MSIDeliveryEngine::hDelivery: Unknown Delivery Failed. Error string from ExecuteMultiProcess No more Mail Exchange Servers to try Unknown error

The setting that needs to be changed is shown below (Smart Host > IP Address/Server Name):

ACTION:
The device that is trying to resolve to the wrong address needs to be changed to the correct address.