Problem with squirrelmail and sendmail queues

Hi,

I have a problem that my queue is increasing because huge amount of
spam generated through apache@localhost and I don't understand a way
to stop it. My front end is squirrelmail and I see spam generated and
the mail sever gets many Mail daemons and deferd mail. And may queue
is nearly 4000-5000 every hour. I would like to know if some body has
faced the same problem and help me out.

The headers of the spam mail headers look like this:
from xxx (xxxx [172.16.1.11])by xxx (8.13.1/8.13.1) with ESMTP id
m3HDXEWG006518;Thu, 17 Apr 2008 19:03:14 +0530
Received: from xxx (localhost.localdomain [127.0.0.1])by xxx
(8.13.1/8.13.1) with ESMTP id m3HD5uxZ027750;Thu, 17 Apr 2008 18:36:46
+0530
Received: (from apache@localhost)by xxx (8.13.1/8.12.10/Submit) id
m3HD42ih027469;Thu, 17 Apr 2008 18:34:02 +0530
X-Authentication-Warning: xxxx: apache set sender to
info@winner.co.uk using -f
Received: from 81.199.47.180(SquirrelMail authenticated user mnvsl)by
webmail.xxxx with HTTP;Thu, 17 Apr 2008 18:34:02 +0530 (IST)
Message-ID: <62877.81.199.47.180.1208437442.squirrel@webmail.xxxx>
Date: Thu, 17 Apr 2008 18:34:02 +0530 (IST)
Subject: FINAL WINNING NOTIFICATION
From: "Uk National Lottery"
Reply-To: claimsofficer_james04@yahoo.co.uk
Bcc:
User-Agent: SquirrelMail/1.4.8
MIME-Version: 1.0
Content-Type: text/plain;charset=iso-8859-15
Content-Transfer-Encoding: 8bit
X-Priority: 1 (Highest)
Importance: High


Please help this is causing lot of problem to manage the mail sevrer.