Logged In: YES 
user_id=113859

This is hard to tell without actually having a working setup
which tries to do this. It might be reasonable, but it would
also assume that this list of "ExternalUser" is hidden at
the right places and does not have to deal with their own
details. 

However I think that request tracker really has a good
concept in this regard
as a requestor only gets mail on certain occasions, but the
bugtracker helps several people to organise these responses.