To enable the Overdue Task Alert, you'll need to complete 2 steps. First you'll need to set the alert on the individual task, then you'll need to set the notification for the users whom you want to receive the alert.
Step 1: Hover over the properties tab, click Property Maintenance, select your property, and the expand the Tasks menu.
Select the task you would like to enable the alert for and then set the alert using the Alert if Left Open field. (Pictured above). The task system will send an email alert for tasks left open exceeding the time selected.
Once you have set the alert, click Save Task.
Step 2: Hover over the users tab, click edit notifications, then select the user whom you would like to receive the alerts
At the bottom of the screen there is a check box labeled Overdue Tasks. Make sure the box is checked and click Save Notifications.
Remember: Users that have this box checked under their notification settings, will receive overdue task alerts only for tasks that are selected to send alerts as set by the system administrator. This feature is best used for a supervisor/managerial roles.