Redirect spam to recipient domain

Hi list.
 
I need to redirect spam to spambox@ some domain. My mailserver is gate
for two domains. So redirecting to [email protected] would redirect
all spam for mydomain2.com to that box also, i dont want that.
 
This is my current setup:
  warn message = X-Redirect-To: [email protected]
 
but it doesnt work the way i want, so i tried this:
 
  warn message = X-Redirect-To: spambox@$domain
 
which results in this:
2004-12-20 10:48:46 1CgK9l-0008L2-OA == user$mydomain.com
R=scan_redirect defer (-17): error in redirect data: domain missing or
malformed in "spambox@"
 
it seems $domain only works in routers? How do i get the recipient
domain in ACL?
 
Best Regards
Tomas Lubkowitz