Deleted message are normally sent to "Deleted Items" folder. You can configure IncrediMail to empty this folder automatically, here's how:
- Click on the Tools Menu > Options > Advanced Tab
- Check the "Empty message from "Deleted Items" folder on exit.
- Click on OK to validate your settings.
Note that you can enable additional settings, such as clearing only the message that have been around your "Deleted Items" for a certain number of days.