I get lots of spam to non-existent mail addresses in my domain.
Every time such a message arrives its bounced back to the spammer.
Now the spammers email address is usually fake which causes the
non-delivery report to bounce back and end up in my (root's) mailbox.
Is there any way to avoid this?
courier doesn't deliver to unknown mail addresses by default. remove
whatever you have in place to accept mail to non existant accounts.