[exim] local user white list

I am trying to verify local recipients from a local (flat file) white
list. I have a router that, I think, should be doing what I want. It
works with -bv from the command line (i.e. fails people not on the white
list), but the messages are still being delivered. What am I missing???

bash-2.03# /usr/local/exim/bin/exim -bv dann.mitton@???
dann.mitton@??? failed to verify: verify_router router forced verify
failure

verify_router:
driver = accept
verify_only
domains = +route_to_domains
local_parts = ${lookup{$local_part}
nwildlsearch{/usr/local/exim/valid.users}{found}{$local_part}}
cannot_route_message = Unknown local user
fail_verify_recipient

MAIL FROM:<>
250 OK
RCPT TO:<Dann.Mitton@???>
250 Accepted
DATA
354 Enter message, ending with "." on a line by itself
Subject: test

test
.
250 OK id=1HtryO-0007Sa-VX
QUIT