Notification settings

Hi Guys I'm having problems with users either getting too many emails or not getting them at all - just to clarify - on the easy discuss home page if they use the subscribe link do they get notifications on all category posts? OR do they have to also subscribe to each category as well? Also I had the settings set to notify all users on New posts but they were recieving 6 copies of the same post? I've turned this off however side admins are now saying that users aren't receiving any notifications even though they are subscribed to the site?