[Exim] Forwad mail via a manual route and allow it to fail.

G'day all,
I have been searching the docs etc but haven't found a sloution to this
yet...

I have a manualroute setup to test my new mail server with some
realistic traffic forwarded from
the current mailserver.

The problem is I don't have all the addresses/domains added to the test
server so I would
like the current exim to just 'forget' deliveries to the test server
that fail.

Is there a way to do this?
TIA.

---Gareth

P.S.

Here is the router on the main server

test_server:
    driver = manualroute
    domains = +local_domains : +relay_to_domains
    route_list = * 10.10.3.3
    transport = remote_smtp
    unseen