[exim] recipient verification callout to specific host

hi,

i want to use recipient verification for mails arriving at our
exim4-gateway. the "problem" is that neither exim4 nor the next
mail-server can verify a local address. the only server that could
do this is our internal mailserver which is not queried.

an incomming mail goes that way:

mail -> exim4-GATEWAY -> stupid VIRUSSCANNER(smtp) -> internalMAILSERVER

i'm now looking for a way to tell recipient verify callout to use
internalMAILSERVER for all localdomains, but couldn't figure out this
ability from the docs.

regards
marko