You can receive bounce messages on a perfectly healthy system, in one of two ways.
1. Some other machine(s) is sending emails and spoofing your address for the return address. In this case the bounces will come to you even though they have nothing to do with you.
2. they are not true bounces, but spam or viruses dressed up to look like bounces, in the hope that you will open them to see why they bounced.
If you have decent AV, Anti Spyware and Firewall, then these are much more likely explanations for your problem. The best answer is a good spam filter.
My spam filter (Mailwasher Pro) filters around 600 fake bounces per day, most of which are well-known.