Unknown senders in outgoing mail queue

We have about 900 unknown senders in outgoing mail queue. We are running Exchange 2003 on Windows 2003. We have been blacklist from some mail servers already. How can I delete the unknown senders in the mail queue? How can I prevent this from happening? How can I find the problem?
mariani_500Asked:
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SembeeConnect With a Mentor Commented:
Go and look at my spam cleanup article

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

That will help you identify what type of messages they are and then how to clean them up.

Simon.
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mariani_500Author Commented:
I'm worried about "Directory Harvest" attacks! Is there any other way around this. Can this be a Trojen? Thanks!
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SembeeCommented:
A directory harvest attack is dealt with using the recipient filtering options that the article mentions. You need to ensure that you have Windows 2003 SP1 installed and enable the tarpit option.

I would be very surprised if it was a trojan. Too conspicuous. Trojans and viruses don't go looking for an SMTP server to send their crap through. They have their own SMTP engine. Using another makes it too easy to find.

Simon.
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