My Exchange 2003 SBS postmaster account is sending spam

I have a small business server 2003 running exchange 2003. Recently the server is sending out lots of NDRs to .co.uk domains (which we do not have contact with).

The subject of all the emails is "One Unread Message" sent to noreply@allianceleicester.co.uk

I thought my server might be under an NDR attack, so I followed steps to turn off NDR notices, enable recipient filtering, and DENY access from the IP address known to be sending these out:
http://www.projecthoneypot.org/ip_195.121.247.24

However after restarting the SMTP server service (as well as GFI service) my mail queue is still being filled with NDR messages and the NDRs are still being sent out, one every 10 seconds. I have Tarpitting set to a 10 second delay so maybe that has something to do with it.

Any insight would be helpful. It could be that I have a virus, but no information appears in google when I try the subject or email address mentioned above. Could one of my SBS clients (25) have a virus and be causing this?
acidgoldAsked:
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MesthaConnect With a Mentor Commented:
Disabling NDRs will not help, so reverse that.
Recipient filtering was the right thing to do, but all that does is stop new messages. It doesn't do anything for the messages that are already on the server. Those needs to be cleaned up.

http://www.amset.info/exchange/spam-cleanup.asp

There is nothing wrong with any of your clients or the server, it just a spammer taking advantage of a default configuration of the server.

Simon.
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acidgoldAuthor Commented:
Thank you for pointing me in the right direction Mestha. I had no idea my server was setup as an open relay... this problem just arose in April 2009 and I have had no incidents since 2005!

I followed the steps on the page you provided to disable my server as an open relay, then used the SMTP connector trick to get all the NDRs into one mail queue on the server and delete them.
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acidgoldAuthor Commented:
Good solution however you could have been a bit more verbose in your comment accompanying the solution.
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