Symptoms

I have created and moved a new process to our production server. It has a destination set of 153 users that an email notification should be sent to. Upon starting the workflow--6 users received an email (verified on our server), and 144 users did not receive the email due to an error stating the email address is not in a valid format.
 

Diagnoses

The Destination was being populated by a SQL call "Get List" method which had a list of User's FQN. The Service Tester returned the correct users for the SmartObject. There was nothing special about the users that were receiving the emails and tasks on their worklist. We also checked View Flow and the user tasks were assigned and Active.
 

Resolution

The issue was related to a Carriage Return character that was in the SQL table where the Destination was being planned from. This caused an issue with the Identity Service and actually created a new Identity.