I recently installed Avast and some receipents are spam filters are having issues with this message in the emails sent. I have Avast 2014.9.0.2013 installed on my system. I followed the instructions in settings> Active Protection> mail sheild> Behavior> unchecked option to insert note into clean message(outgoing) to disable the message. After changing the setting I even rebooted my pc and it is still being inserted.
Any ideas.