Is the Zimbra-Spamfilter filtering only normal accounts or is it filtering delivery lists as well?

If it's filtering normal accounts only - how can I forward emails to an external adress but have them spamfiltered and virus checked first? Is there any way to do this with Zimbra?

If a create a normal account and activate forwarding everything's forwarded (including spam).

I'm using Zimbra 4.0.1 on Debian Testing.