How can users get automatically emailed when I respond to them?

[Citizen]

I need to have the system automatically email specific usergroups posting in certain forums when we reply to their threads. Is this possible?

-Cit

[iogames]

every user can have instant notifications of he threads they are interested via Options on User cP... it's that what u r looking for?

[Citizen]

Yes, but is there a way to simply have them emailed every time we post in their thread for specific forums?

[iogames]

Let me see if I understand :erm:

The 'Instant Notifications System' will email to any user that choose to watch the threads they're interested to...
So I know about EPC Mailer, but I think you're complicating the process... [it was $5 usd now it's OpenSource but have some bugs, so I will suggest Instant Notification System :P]

[Citizen]

How can I make sure that that is enabled? And what do they have to set it to? Because my users are complaining that they have enabled all of the stuff in their cp but they are not getting notified.