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?
Undo whatever you did to force Courier to accept mail to nonexistent local
mailboxes. Courier, left to its own devices, rejects mail addressed to
nonexistent local recipients.