In Planbox you can set email notifications per initiative. The email will be sent out on the same dates as the due dates. If you want customized reminders, you can have that by integrating your Planbox work calendar with Google or Outlook calendar (or any other calendar system that supports the iCal interface). You can then configure the reminders and notifications as you want in the calendar you share.
The calendar is live synced so you will have to do this once. You will be able to share due dates (note that only tasks with due dates are shown in the calendar) and the iterations of the Initiatives you participate in and modify the reminders in the integrated calendar. The current version is a one way calendar sync. Only changes made in Planbox are reflected in the calendar you share. Changes made to the shared calendar will not result in any updates in Planbox.