well if you get email and they do not we know the server mail works so it can only be a couple things.
1. You do not have notification enabled in admin
2. They are not subscribed to be notified
3. Emails are being sent and they are in there spam folders
I think that covers all the possible scenerios. Notifications on who gets notified are stored in the pp_notify table and we get that userid and check the pp_userid table and get there userid. There is nothing major required here only that you have notification turned on in your admin settings and that users elect to be notified.