[exim] Whilelisting a single IP

Hi !

I'm trying to whitelist an IP that is listed on a RBL ( dnslists ) the IP I'm trying to allow is a nat IP that is used by
several clients so it's unsafe on one of my RBL servers. the host I'm trying to whitelist is: natsp-43-netra20.ice.co.cr
I have tried this:

check_recipient:
  # Exim 3 had no checking on -bs messages, so for compatibility
  # we accept if the source is local SMTP (i.e. not over TCP/IP).
  # We do this by testing for an empty sending host field.
  accept  hosts = :
  deny    !hosts = natsp-43-netra20.ice.co.cr
          dnslists = relays.visi.com:bl.spamcop.net:relays.ordb.org:sbl-xbl.spa
          message = host is listed in $dnslist_domain

  accept  domains = +local_domains
  accept  hosts = +relay_hosts
  accept  hosts = +auth_relay_hosts
          endpass
          message = authentication required
          authenticated = *
  deny    message = relay not permitted

but I still get the message 550 Host is listed on bl.spamcop.net anyone could tell me exactly what is my problem
TYVM !

Chuby007