A lot of our users are commenting on receiving spam from themselves. when we look at the full header it from an external spammer masquerading as the user.
has anyone else notice this & if so any suggestions?
Thanks.

e.g. replaced user by a.user@server.com

Code:
X-Spam-Score: 0.744
X-Spam-Level: 
X-Spam-Status: No, score=0.744 tagged_above=-10 required=4 tests=[AWL=-4.800,
	BAYES_50=0.001, DNS_FROM_RFC_WHOIS=1.447, DRUGS_ERECTILE=0.493,
	HTML_EXTRA_CLOSE=3.6, HTML_MESSAGE=0.001, MIME_HTML_ONLY=0.001,
	UNPARSEABLE_RELAY=0.001]
Received: from ([127.0.0.1])
	by localhost ([127.0.0.1]) (amavisd-new, port 10024)
	with ESMTP id dvBJy5Xor6-0 for <>;
	Wed, 26 Sep 2007 19:56:03 +0100 (IST)
	id 5D1E41620002; Wed, 26 Sep 2007 19:56:03 +0100 (IST)
Received: from ip-89-102-153-143.karneval.cz (ip-89-102-153-143.karneval.cz [89.102.153.143])
	by  (8.13.6/8.13.6) with SMTP id l8QIrDTi007203
	for <a.user@server.com> Wed, 26 Sep 2007 19:53:13 +0100
Date: Wed, 26 Sep 2007 19:53:13 +0100
Received: from Dina Love (10.11.17.13) by ip-89-102-153-143.karneval.cz (PowerMTA(TM) v3.2r4) id hfp75o25d55j94 for <a.user@server.com>; Wed, 26 Sep 2007 08:53:12 +0100
Message-Id: <20070926095312.3049.qmail@ip-89-102-153-143.karneval.cz>
To: <a.user@server.com>
Subject: RE: September 70% OFF
From: "******.com Inc" <a.user@server.com>
MIME-Version: 1.0
Content-Type: text/html; charset="iso-8859-1"
Content-Transfer-Encoding: 8bit
X-Antivirus: avast! (VPS 000777-0, 26.09.2007), Outbound message
X-Antivirus-Status: Clean
X-Virus-Scanned: by amavisd-new