I use a ZyXEL USG200 firewall and I have to put in it the b.barracudacentral.org URL to activate the check of incoming mail. I use an external ISP DNS server and an external hosted email service, both outside the LAN controlled by the above firewall.
www.barracudacentral.org service require that "I register the list of IP addresses of your domain name servers (DNS servers) that will be making queries.".
I think that I have to register the IP address of my firewall that queries the b.barracudacentral.org service, and not the DNS or email external services.
It is correct my assumption ?