It's probably trouble with your provider. Last year, I stopped receiving notifications and found it to be a Comcast issue. So now I use my Hotmail account and I get ever one of them.
From my experience in administrating other forums, the odds are about 99% that it is an issue with your email provider. If you contact them they can resolve it for you. Forum emails often result in being flagged as spam due to the amount of email one can receive from them..
I use a gmail account for those forums that allow it to prevent this...