You can set up, at the customer level, automatic task reminders.

Requirements: You must have a customer role at the customer level that includes the Modify Customer user right.

Up to three reminders are provided, each with a different subject, message and sending date relative to the due date of the task. 

The date options for sending task reminders are:
The last option, After Due Date, sends a daily reminder until the task is completed. The user can also define a specific hour of a day for sending the reminder. If a task is created after the reminder date, no e-mail message is sent for the reminder.

Tip: If you do not want the automatic task reminder to be sent from a specific task, you can define it when you create a task. In the Task Options area, select the Exclude task from automatic reminders check box.
  1.  From the Customer menu, select Manage Task Reminders.
  2.  Define task reminder dates, reminder messages, and reminder time as necessary.
    Tips: You can use tags to insert variables in the task reminder messages. The following tags are available to be used:
    • <projectName>
    • <taskTitle>
    • <taskDescription>
    • <taskDueDate>
    Note: The time specified is based on the server time.
  3.  Click Apply.