As a default value, when an user registers, the option for the "Watch threads when creating or replying:" is "Yes, with email". However, some users wanted to disable that and just receive alerts on site. I've advised them to go to Account > Contact Details and uncheck Receive site mailings. Even after doing so, they still got email notifications from the watched threads. I've tested this myself and they're right. Is there a possibility of disabling (for a user), the email notifications?