Use hmail_spamfilter.

spam eg:
Return-Path: b@192.9.9.11
Received: from localhost by XP_model with SpamAssassin (version 3.2.3); Mon, 22 Feb 2010 14:43:35 +0800
From: <b@192.9.9.11>
To: <abc@192.9.9.88>
Subject: *****SPAM*** dddd
Date: Mon, 22 Feb 2010 06:43:30 +0000
Message-Id: <f8f1aeff3de7a5131180133801006092@192.9.9.11>
X-Spam-Flag: YES
X-Spam-Checker-Version: SpamAssassin 3.2.3 (2007-08-0 on XP_model
X-Spam-Level: *********
X-Spam-Status: Yes, score=9.1 required=6.3 tests=AWL,FH_DATE_PAST_20XX, RCVD_NUMERIC_HELO,RDNS_NONE,TVD_RCVD_IP,TVD_RCVD_I P4,TVD_SPACE_RATIO shortcircuit=no autolearn=no version=3.2.3
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="----------=_4B822797.FBB60000"
X-hMailServer-Spam: YES
X-hMailServer-Reason-1: Tagged as Spam by SpamAssassin - (Score: 9)
X-hMailServer-Reason-Score: 9

hi rosali:
i use hmailServer+Roundcube+SpamAssassin to build my email server.they run very well.now i have a question：when the server Received a spam（used SpamAssassin），how can i config to take the spam into the junk folder in Roundcube automatically.Thanks.