Description of the problem
If you have enabled all the available global email notification settings as well as user-level notifications:
However, the problem is that you still do not receive email notifications when ticket is either created or updated by the client.
Solution
To fix this problem, you (or the Redmine administrator) have to add the Redmine user you are logged-in with to be a member of the project where the Helpdesk is used (and enabled as a module). You have to go to Administration - Users - [select the needed user that has the notification problems] - Projects tab. Now add the Helpdesk project. Please see this picture to make the situation clear.
Now everything will be fine and the support engineer (user Stephen from the above example) will receive email notifications successfully when the ticket is updated by the client.