[exim] Verify outgoing email while using a smarthost

Hi,
Is it possible for Exim to verify outgoing mail when using a smarthost?
Specifically, I'm looking to have Exim verify (using dnslookup) that the
domain exists for the recipient. If the domain returns NXDOMAIN (or some
other DNS error), defer it, if DNS exists, continue with the routing. I
tried the following:

# Verify the recipient domain exists in DNS before sending to the relay.
verify_address:
debug_print = "R: verify_address for $domain"
driver = dnslookup
domains = ! +local_domains
verify_only

smarthost:
debug_print = "R: smarthost for $local_part@$domain"
driver = manualroute
domains = ! +local_domains
transport = remote_smtp_smarthost
route_list = * DCsmarthost byname
host_find_failed = defer
same_domain_copy_routing = yes
no_verify
no_more

And it seems to work during testing:

# exim -bv someone@???
someone@??? failed to verify: Unrouteable address
# exim -bv someone@???
someone@??? verified


However, when sending a test message to an NXDOMAIN, exim happily forwards
it to the smarthost:

2016-08-03 08:07:28 1bUvtQ-0007bm-Vh <= root@somehost U=root P=local S=486
T="test"
2016-08-03 08:07:29 1bUvtQ-0007bm-Vh =>
someone@??? R=smarthost T=remote_smtp_smarthost
S=505 H=ses-smtp-prod-335357831.us-east-1.elb.amazonaws.com[50.19.94.229]
X=TLS1.2:DHE_RSA_AES_128_CBC_SHA1:128
DN="C=US,ST=Washington,L=Seattle,O=Amazon.com\, Inc.,CN=
email-smtp.us-east-1.amazonaws.com"
2016-08-03 08:07:29 1bUvtQ-0007bm-Vh Completed

Is it possible for Exim to do outbound verification while using a
smarthost? If so, what am I missing?

Thanks