Groupwise 2012 sp1 - Calendar invite not notifying user(s)

In Groupwise 2012, if a user creates a calendar invite, users are not notified. For example -
1) Go into the Groupwise Calendar
2) Double click a day and time. This opens the Posted Appointment dialog box.
3) User clicks on options and adds users in the contacts section.
4) User goes back to appointment tab and makes the appointment. (Notify Recipients is checked and grayed out)
5) User clicks POST. But none of the contacts get any notification.

What are we doing wrong, or is there a bug?

Thanks