Postfix comes with a binary named 'sendmail' which simulates the original sendmail's behavior. This is for compatibility reasons because many Un*x components require sendmail.
However, the files you would normally find below /etc/mail are the sendmail configuration files. Those are only present if you really have sendmail installed. With Panther they are not there because you run postfix, not sendmail (even if there is a sendmail 'simulator' this doesn't mean you have sendmail installed). Since postfix is configured in an entirely different way than sendmail, you should skip this section in your tutorial and better find another one which covers the postfix configuration.
