If you have the basic product offering, to update where your filtered mail is delivered, you would email email@example.com and request they update your "Email Routes" for your domain in Awesome Antispam. You would provide them the mail server(s) you'd like email delivered to.
If you have the premium offering this is managed from within the web interface after clicking on the "Edit Routes" icon:
With the "Edit Routes" function you find the route(s) (destination mail server) and their respective delivery order.
You have the option to add and delete routes. Also, the list allows you to dynamically move the order of the routes by drag dropping them to the right position in the list.
Whenever there are temporary problems with the first route (e.g. 4xx temporary rejects), we'll automatically try delivery to the second route (etcetera). If there are permanent failures with a route (e.g. hostname not resolvable) we'll directly start queing email and won't try the next route. We recommend not to use your own fallback system, and instead use the filtering cluster to queue your emails if there are problems with your main destination route.