It sounds like you may be confusing the sendmail access file with how an access file is used and specifed in postfix.
The postfix access file is more of a specification on how to specify checks within postfix that can be performed at different stages of the smtp transaction. So the file /etc/postfix/access is not read by postfix by default, it must be specifed in one of the check_*_access tags in main.cf. Like what I mentioned in my post.
# Checks performed after connect from MTA
# Checks performed during HELO handshake
# Checks performed after MAIL FROM
# Checks performed after RCPT TO, but prior to DATA
1) Each check_*_access listed specifes a different file. The contents of each file conform
to the postfix access file specification mentioned in the top of /etc/postfix/access. So in your case, you would need to specify your access file in one of the check_*_access entries.
2) In my case, each check is specifed at different stages of the smtp transaction, but most can be combined under the smtpd_recipient_restrictions= stage. In fact, its actually more effeciant to combine all checks under smtpd_recipient_restrictions. I chose not to - to help battle dictionary attacks that were clogging my logfiles and skewing my daily stats.
Finally, once you feel comfortable in using the postfix access file and how to apply them to checks_*_access, take a look at adding regexp and pcre to the mix. Regular expression syntax (especially the perl based ones, pcre) are incredibly powerful in combating spam and viruses. I use them to help block MTA's from residential (dhcp assigned) IP addresses that SORBS does not catch.