no, "management" vs. "application" messages is not where the line should
be drawn. Return-Path is provided so that applications can use it when
it's appropriate. Most automatic responses should go to Return-Path.
What if there are multiple addresses in From: and Sender: was just the
messenger, or what if From: is a group address?
that's part of why sending the response to the return-path address is
better - it's more likely to reach someone who can actually make use
of the response.
The application acks fall
apart if basic features of the messaging network are used but the
application sends its ack to the node instead of the application
if the sending application is putting anything in the MAIL FROM
field other than an address which will reach the sending
application, the sending application is broken.
Keith