To actually use this software after package installation you need to configure postfix to use it

Edit postfix configuration files:
put somethink like the following into /etc/postfix/main.cf:

smtpd_recipient_restrictions =
  reject_unlisted_recipient
  ...
  reject_unauth_destination
  check_policy_service 127.0.0.1:10001

For the size acl to work correctly, apolicy need to be called this way:

smtpd_end_of_data_restrictions = check_policy_service 127.0.0.1:10001

edit the example acl /etc/apolicy/policy.conf to adapt to your environment.
remember to enable and start the apolicy service:
chkconfig apolicy on
service apolicy start
or postfix will fail.