How to disable this email has been sent from a virus free computer protected by avast message
All you need to do is disable Avast signature Feature on avast 2016.
1> Right-click Avast Free Antivirus icon in the system tray and go to “Open Avast user interface”.
2> Now click the gear icon in the top-right corner.
3> Next, uncheck “Enable Avast email signature” and click “OK” – That’s it !