Logged In: YES 
user_id=6405

I believe that the "anonymous" users you want to have can be handled  
right now by having automatic registration of unknown users in the  
mail gateway, but having their initial Role be set to something with  
almost no Permissions. Then all the current mechanisms work just  
fine, including the sender identification and nosy lists.  
 
Please indicate whether this is reasonable or not - I probably won't 
have time to evaluate "request tracker" for some time.