[mcnallym]

If your DNS is held externally then the DNS Proxy on your gateway won't be used. Your DNS requests will not be sent to you but your DNS Hosting company.

ISP Redundancy does really need to use an internally hosted DNS Server to work correctly as designed, so that it can use the DNS proxy. However what you can do is create 2 A Records with different hostnames

You will then need to make your MX Record point at both A Records, with ISP-1 IP address having a higher priority. This will ensure that if ISP-1 line fails then mail will be sent to the secondary address.

I am not aware that your DNS Hosting company can tell if your line is down so A records for other services will only have 1 IP address for them and so won't failover. This is why Check Point say to host your own DNS Server so that the requests for DNS lookups are sent through the firewall where the DNS Proxy can intercept A record lookups and pass on things like MX Records to the DNS Server.

If the only service you have is Mail then not a problem as you can use a lower priority for the second IP address in the MX Record.

Hopefully this makes sense.

Michael McNally.