Fair enough, and I now understand the issues with root receiving and handling emails. The problem with the alias is that ALL emails are being sent out to my ISP, and on to the particular user.
Even for local users that are in /etc/passwd?
I would like to make this user receive emails locally only, obviously not root (for all the very good reasons you pointed out), but some other non-privileged user. I don't know how to get a user setup only for local only delivery to the machine in question, not sent out of the local network.
So something in the postfix configuration is telling it to send mail elsewhere. Have you changed the postfix config at all? Because usually it is happy to deliver local mail for local users. The aliases file should have something like
root: chuck
where 'chuck' is the local user; that will put the message in /var/mail/chuck. There's a postfix config variable called 'local_recipient_maps' that determines what is a local recipient - but the default uses, amongst other things, the standard unix passwd file.
P.