This simple functionality sends an automatic email to a user when due dates are approaching, late, or marked complete. The system should allow the administrator to set rules regarding the frequency and timing of these emails.
Scenario: A global consulting firm uses CPM software to manage and monitor its annual budget build. Each budget involves several collaborators from various departments.
Solution: The finance team uses the software to assign tasks and automatically remind users when actions are required. This saves the finance team from having to notify each of these users separately when tasks are past due or have just been assigned.
It is important in any business process to avoid sending too many emails to users. They'll start to ignore the messages, and you'll be back where you started. For this reason we prefer task management tools that allow us to limit the amount of reminders that go out. Another alternative is to only allow the system to send an email when an admin triggers it. For example, if budgets are due today, the admin can review who is past due and only trigger nag messages to those people.
While this requirement is specific to email notifications, there are plenty of other mechanisms. IM? Text? Push notifications via an app? If the vendor provides that, awesome.