I'm not sure where to post this, but I do need some advice. Based on the number of "Mail Delivery Subsystem, Returned mail: User unknown" I have started to get, it's become obvious that some spammer is using my email address from my domain here as his spammer return address. The first sign was a couple weeks ago when I got a "refused delivery" form back from an ISP saying that I was a "known spammer". That confused me, but the Returned Mail I am getting confirms my suspicions.

Is there anything I can do about this? I have looked through the mail headers, and the replies are all coming from AOL via lunarpages to my forwarding address, and there doesn't seem to be a way to figure out who the real sender is.

Thanks for any advice!

Yes, unfortunately it is critical. It is the only way 99% of the world can reach me, since I set up my domain just to avoid ever changing email addresses if my underlying ISP changed.

Here's a header I got today. I don't fully understand each line:

X-Apparently-To: dgf@sbcglobal.net [my forward] via web80411.mail.yahoo.com; 31 Jul 2003 17:07:34 -0700 (PDT)
X-YahooFilteredBulk: 64.235.234.121
Return-Path: <>
Received: from vmc-ext.prodigy.net (207.115.63.88)
  by mta813.mail.yahoo.com with SMTP; 31 Jul 2003 17:07:34 -0700 (PDT)
X-Originating-IP: [64.235.234.121]
Received: from taurus.lunarpages.com (taurus.lunarpages.com [64.235.234.121])
   by vmc-ext.prodigy.net (8.12.9/8.12.3) with ESMTP id h7106Y6t666612
   for <dgf@sbcglobal.net>; Thu, 31 Jul 2003 20:06:52 -0400
Received: from [205.188.159.1] (helo=omr-d03.mx.aol.com)
   by taurus.lunarpages.com with esmtp (Exim 4.20)
   id 19iNRx-0003DK-5u
   for david@fridley.net [my domain address]; Thu, 31 Jul 2003 17:07:13 -0700
Received: from  str-m01.mail.aol.com (str-m01.mail.aol.com [172.21.28.97]) by omr-d03.mx.aol.com (v90_r2.6) with ESMTP id RELAYIN1-0731200556; Thu, 31 Jul 2003 20:05:56 2000
Received: from localhost (localhost)
     by str-m01.mail.aol.com (8.8.8/8.8.8/AOL-5.0.0)
     with internal id UAA12242;
     Thu, 31 Jul 2003 20:05:55 -0400 (EDT)
Date: Thu, 31 Jul 2003 20:05:55 -0400 (EDT)
From: Mail Delivery Subsystem <MAILER-DAEMON@aol.com>
Message-Id: <200308010005.UAA12242@str-m01.mail.aol.com>
To: <david@fridley.net>
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
   boundary="UAA12242.1059696355/str-m01.mail.aol.com"
Subject: Returned mail: User unknown
Auto-Submitted: auto-generated (failure)
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname - taurus.lunarpages.com
X-AntiAbuse: Original Domain - fridley.net
X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse: Sender Address Domain -

Are you running a FormMail script, or any other type of mail script where the recipients are in a hidden form field, or any mail script where the user can set the recipient(s)?

Unfortunately, I'm afraid there's little you can do except legal means.  SMTP protocol allows a email message use any address in the FROM field, even it is invalid. My yahoo address was once used by spammers. One possiblity is the spammer  got my email address from the Internic domain registration database -- the one publishes each domain name and its administrative/tech contact.