main.cf:
smtpd_restriction_classes =
   greylist


smtpd_recipient_restrictions =

    check_sender_access pcre:/usr/local/etc/postfix/greylist.pcre
    check_helo_access pcre:/usr/local/etc/postfix/greylist.pcre
    check_client_access pcre:/usr/local/etc/postfix/greylist.pcre