0022721: Start using smtpd_relay_restrictions

Migrated from: https://tracker.clearos.com/view.php?id=22721

Reported by: NHowitt

Round about v2.10 of postfix, a new parameter smtpd_relay_restrictions was introduced. This allowed the separation of open relay control from the smtpd_recipient_restrictions, leaving the smtpd_recipient_restrictions for anti-spam measures only by removing reject_unauth_destination from one of its settings.

The line: smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination

can take the place of the reject_unauth_destination in the smtpd_recipient_restrictions.

This would reduce the chance of a user inadvertently creating an open relay by adding parameters to the smtpd_recipient_restrictions in the wrong order.

Note this may be an app-mail bug as I am not sure which does the initial settings.