spam using my domain name

I get catchall from a couple of my domains in the thousands in the form of  postmaster's delivery status notification failure reports or blocked spam messages. In the example below the origionator sent with from: dac@MY-DOMAIN.com . Though this did not come from my web or mail server, because the used @MY-DOMAIN.com in from field I get these in catchall. I use catchall extensively to give out my email specific to purpose it was used for and as aliases for business use. I hate that I am getting all thesed returned spam, and that thousands of more people are getting spam from my domains. Though I have many more domains this occurs with just 2 of them so far. Any suggestions experts. Desperate. Thanks

Received: from dsl-203-33-163-29.NSW.netspace.net.au ([203.33.163.29]) by HELIODOR.agatesoftware.local with Microsoft SMTPSVC(6.0.3790.1830);
       Fri, 22 Sep 2006 21:08:33 -0400
Received: from [203.33.55.191] (helo=pwr)
      by dsl-203-33-163-29.NSW.netspace.net.au with smtp (Exim 4.43)
      id 1GQw1g-0006TS-9T; Sat, 23 Sep 2006 12:09:52 +1100
Message-ID: <001f01c6deac$cae08279$bf3721cb@pwr>
From: "Albert Sanchez" <dac@MY-DOMAIN.com>
To: <aafkj4btroy@agatesoftware.com>
Subject: future tense
Date: Sat, 23 Sep 2006 12:00:13 +1100
MIME-Version: 1.0
Content-Type: multipart/related;
      type="multipart/alternative";
      boundary="----=_NextPart_000_001B_01C6DF00.9C8C9225"
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2800.1106
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106
Return-Path: dac@MY-DOMAIN.com
X-OriginalArrivalTime: 23 Sep 2006 01:08:33.0738 (UTC) FILETIME=[CA5B9AA0:01C6DEAC]