• I think redmine can be more smart when not project found for an incoming email. Now the email is only marked as seen, and no issue is created. This way we need to review periodically de the inbox to find non processed email

I think redmine would try:
-check the 'from' email address, and create a task for the user without project. This way the user will be the issue in your main page as minimum. If the missing project is a problem, redmine can use an internal project as a 'catch-all' (aka 'Null Object Pattern'). You can name it 'missing_project' like the ruby's missing_method

• as a plus, redmine cand check CC addresses to 'compute' posible projects searching for projects with all the users in from & CC fields