Cannot send notifications to intended user

When a user has their content updated, the message module and one of its modules is called with the parameters ($destination, $message, $params = array()). However, I was initally not receiving any notifications because I though my local machine settings are probably not set up very well but later when I tried to implement a module to send messages to the watchdog, the destination was found to be null. Now I'm not sure if this should go in the messaging module issues or here so I just chose this (plus I'm assuming that since Messaging was fully unit tested).