Question on Exchange 2003 security

[DavidSnell]

I have received the following types of spam and would like everyones opinion as to whether or not I have a security issue with my Exchange server or SMTP services. The header info follows:

Microsoft Mail Internet Headers Version 2.0
Received: from exchange.xyzdomain.com ([66.215.255.73]) by xyzdomain.com with Microsoft SMTPSVC(6.0.3790.211);
Tue, 22 Feb 2005 11:02:35 -0500
Message-ID: <07ae01c518f8$f801353e$2f28efe4@Penguin>
From: "Joshua R. Schelske" <david@xyzdomain.com>
Bcc: <david@xyzdomain.com>
Subject: Windows XP & Office XP for $80
Date: Tue, 22 Feb 2005 08:00:43 -0800
MIME-Version: 1.0
Content-Type: text/html; charset="ISO-8859-1"
X-Priority: 1
X-Mailer: PHP
Return-Path: david@xyzdomain.com
X-OriginalArrivalTime: 22 Feb 2005 16:02:36.0140 (UTC) FILETIME=[ECF512C0:01C518F7]

Please note that xyzdomain has replaced my actual exchange domain. The IP address reflected above is the original from the email and is NOT my public IP.

I've received a number of these emails and if there is a security hole can someone point me in the correct direction to correct it?

Thanks for all your assistance.

David