How do drop emails coming in that do not have an associated email address

Hi
I am getting quite a few emails to admin that are saying the Fred.Blogs.123@domain.com has sent an email and is being bounced as spam, the user is not a valid user, and I suspect this is a spoofed email.
My mail-check report is 10/10, I haveno open relay as everything is checking out fine with all online test. And I have checked server logs, and no email has been genereated from my server.

So how can I auto drop these emails that are arriving so that admin does not even see them, as they are unknown users to domain.

Any Ideas?

IDC