[Dovecot] Delivering message to other mailbox

[Frank de Bot]

Hi,

On my mailserver I have for each mailbox a sieve script to put 
Spam-marked message into a folder (match header, then fileinto 'Spam').

This works, but I want to deliver spam-marked messages to a different 
mailbox.
For each user a seperate mailbox is created next to the existing 
mailbox, allowing different authentication.

How can I do this with dovecot/pigeonhole? I figured out I could 
redirect is the user.spam at domain which delivers to the other mailbox, 
but it will go into a new delivery process with amavis set up. (There's 
no point to scan a single message twice).

Is there a way I can accomplish to directly deliver a spam-marked 
message to a different mailbox?

Regards,

Frank de Bot