It is a common practice for trojans, viruses, worms and spam email to spoof a fake return address. It has nothing to do with your use of VisNetic MailServer and there is nothing that you or anyone else can do about it. It is already a federal offense to spoof a return email address, yet that does not seem to be stopping the practice.
Unless you are running an open mail relay, any spam or virus laden email bearing your return address will not be seen as originating from your domain. The IP address from which the email originated is what triggers a domain being blacklisted, not an obviously spoofed return address, so you should not be a concerned about being blacklisted.
Possible reasons you may receive spoofed return messages are from an anti-virus program installed/setup by a system administrator on a different mail system, or typically from spam messages using your return domain. The practice of returning emails detected as a virus is optional with any properly written anti-virus program and usually a system administrator will not enable that option simply because it is common practice to spoof the return email address. The process of returning emails to a spoofed address (and the subsequent return of that email by the spoofee because it was probably addressed to a non-existent address) typically causes more problems than the virus payload. Spoofed return addresses from spam messages are more common and nearly impossible to avoid. Your best defense is to reject unknown users to your domain (Domain - Domain tab - Unknown users section) and when possible filter (use content filtering) on common return message notification strings (undeliverable in subject, etc...) to filter these types of messages to an account checked by your administrator.