I have started again to use Spamsieve since the amount is rising.
From my past use I know there is a way to get Spamsieve to drop the detecteer spam into the regular spambox that Apple creaties as a spambox. So then it is located in the Postboxes section and no longer in the "On my Mac" boxes.
However I cannot retriever the message how that should be done. So if anyone can post it then I am thankfull.