[exim] delivery to IMAP subfolder?

Hi,

I am using exim for a virtual hosting environment. There are multiple
domains with multiple email adresses. Everything is set up fine. Now I have
spamassassin included in it as well.
Now I want the possibility to deliver mails, that are marked as spam, into
a subfolder of the normal inbox (the inboxes are Maildirs). Since I am
using an IMAP-Server the mailboxes are already prepared for this. The only
problem I see is, that exim doesn't know about the IMAP subfolders.

Any hints how I can still achieve this funktionality?

Regards
Marco