Job,

AK deliver mails statically via IP. In your scenario, I'd propose a round robin whereby we shall create an A record resolving to both AKG and JTL IP addresses. In the event the AKG link goes down the server will be reachable on the JTL IP and mail flow will not be interrupted. You may not that outbound will be interrupted if you use AKG smarthost as it does not allow relay / not open for relay. To be able to deliver you may opt to relay via DNS of either ISP.

You may contact our support on 3600200 for more.

Kihanya
AKG

Wouldn't a better solution to OPs problem be to setup an MX record with lower preference pointing to JTL? He only wants to use JTL as a backup link.