Re: Notification emails not being sent for one site
There is no such feature OOTB in alfresco. Alfresco doesn't send any email notifications on file uploads. There is no settings or configuration in admin tools either to setup these notifications. It must be some kind of custom rules/ custom behaviors which you would crerate to listen to content upload event and notify the user.
You may have to check your source code to see if you have created any behavior or rules to handle this event. You may also check folder rules configured per site as well. Its totally custom code/configuration.