[Exim] how to skip a router for local mails?

Easy one, 2 parts -- Exim 4.04:

1) how do you skip a router if the email was sent from one user to
another within the domain? I have the spamassassin router configured,
but I don't want it to scan any internal mail (bob@??? ->
staff@???):

current config:

   spamcheck_router:
     no_verify
     check_local_user
     condition = "${if and { {!def:h_X-Spam-Flag:} {!eq
{$received_protocol}{spam-scanned}}} {1}{0}}"
     driver = accept
     transport = spamcheck

Reading the Routers generic options section, what I think I want is the
*reverse* of the "domains" keyword? Or possibly some sort of
"condition" test?

2) given the above router, should it go above, or below, the
system_aliases router in my config? Or should it belong at a different
spot entirely?

Thanks! A major problem happening is that "joe@???" sends an
email to "staff@???", an alias which expands to a bajillion
addresses. Then, each mail to each individual address is sent through
SpamAssassin, just clogging up the works entirely. In a nutshell, I
want anything sent from my local domains not spamcheck-touched.

I'll get this all figured out one way or another... :)
-te

--
Troy Engel, Systems Engineer