currently, when I reply to a redmine task notification by mail from an unregistered email (forget to change my "from" account), I get an ugly bounce:

                  The mail system

: permission denied. Command output: Request was
   denied by your Redmine server. Possible reasons: email is sent from an
   invalid email address or is missing some information.

it would be very nice if instead of bouncing that mail, Redmine would send a normal notification of not having enough privileges