{% if smtp_relay_host and smtp_from_relay_allowed %}
domain ip {
    # Accept incoming connections on port 25 from SMTP relay host.
    table filter {
        chain INPUT {
            # SMTP for server communication.
            proto tcp dport 25 {
                saddr {{ smtp_relay_host }} ACCEPT;
            }
        }
    }
}

{% if lookup('dig', smtp_relay_host + '/AAAA') not in ['NXDOMAIN', ''] %}
domain ip6 {
    # Accept incoming connections on port 25 from SMTP relay host.
    table filter {
        chain INPUT {
            # SMTP for server communication.
            proto tcp dport 25 {
                saddr {{ smtp_relay_host }} ACCEPT;
            }
        }
    }
}
{% endif %}
{% endif %}