Basic spam filtering in postfix

I was starting to set some basic spam control in our mail server
(postifx in RHEL 3). So, based on
http://www.unixwiz.net/techtips/postfix-HELO.html and
http://www.freesoftwaremagazine.com/free_issues/issue_02/foc us_spam_postfix/,
I added to main.cf:

smtpd_delay_reject = yes
smtpd_helo_required = yes
smtpd_helo_restrictions =
permit_mynetworks,
warn_if_reject,
reject_non_fqdn_hostname,
reject_invalid_hostname,
check_helo_access
hash:/etc/postfix/helo_access,
permit

Where helo_access looks like this:

domain.com REJECT You do not belong to our domain

But, the last spam message I got claims to have a return path of
info@domain.com and is addressed to sales@domain.com, a non-existent
account. Why wasn't it dropped?

--
Mauricio raub-kudria-com
(if you need to email me, use this address =)