Have you got the option for the notifications by email selected?
If you dont no
how to check heres how:
1. go to quick links
2. go down to the messaging & notification section
3. go to the part with the title "Default Thread Subscription Mode" (in blue writing)
4. in the bottom right corner of that box theres a drop down box.
5. check which setting you have it on as there are several.
6.
problem solved
If its not that then i dont know and admin/moderator will know
Hope this helps