Set `smtpd_relay_restrictions` to backwards compatible mode. Resolves #231.

roles/mailserver/templates/etc_postfix_main.cf.j2

 broken_sasl_auth_clients = yes
 smtpd_sasl_security_options = noanonymous
 
+# set to empty value for backwards compatibility
+# as per http://www.postfix.org/postconf.5.html#smtpd_relay_restrictions
+smtpd_relay_restrictions =
+
 smtpd_recipient_restrictions =
   permit_sasl_authenticated,
   permit_mynetworks,