Question:

Why is a user receiving duplicate email notifications in Vault?

Answer:

The user is receiving two different emails. One is a Task Reminder Notification,. The other is a Task Over Due Notification configured on a Document workflow step. 

• Task Reminder Notification - This is a Job that is set up to run daily at 5:00 AM. It utilizes the task_reminder_notification__v Document Message.
  
  
  
  
• Task Overdue - This is the notification being sent from the workflow step to notify the user the task is overdue. This utilizes the task_overdue__c Document Message.
  
  

Related Documentation:

Vault Workflow Documentation: Configuring Document Workflows: Workflow Task & Decision Steps