fix: add 'smtpd_relay_restrictions' parameter to the Postfix config

tasks/configure_postfix.yml

@@ -8,4 +8,7 @@
     block: |
       # non-default
       mydomain = {{ ansible_domain if ansible_domain else 'localdomain' }}
+      smtpd_recipient_restrictions =
+      # smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, defer_unauth_destination    # DEFAULT according to `man 5 postconf`
+      smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, defer_unauth_destination
   notify: restart postfix