Mail queue filling up on Windows SBS 2003 server

I have a Windows Small Business Server 2003 server with the mail queue filling up and depleting hard disk space on the server.  The exchange server logs grow to more than 1GB.  I have verified that the server is not an SMTP relay.  One thing I noticed is that in the ESM Queues, every Queue shows the sender as ""<".  How do I prevent this constant mass emailing? I have checked each PC and server on the network for viruses/spyware and confirmed that we are clean.  Does this sound like it is malware related?

Rick Ferreira
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I think there will be some malware on your clients, because it's easy to find out if you have an open relay. If you want to just give me your IP and I'll check.
I'd suggest to find out which computer opens SMTP connections to your server (

If you've not enabled anonymous mailing, you should be able to find out who sends out your mass mails (normally, a SBS sends statistics each day/week).
here is what you might want to do:
What anti spam software are you using

This is definitely spam attack

Go to and test if you are open relay

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Alan HardistyCo-OwnerCommented:
If the sender is a 3rd party on your server then you are an Authenticated Relay.
Please have a read of my article for what to do and how to identify the user / password that has been compromised, change the password, restart the SMTP service and then empty your queues.'t-send.html 
You will also need to get yourself off the Blacklists after you have solved the problem.
You should then instigate Account Lockouts on your server to prevent accoutns from being brute forced and then force regular password changes to stop this sort of attack from happening again,

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Barry GillChief of StaffCommented:
this is part of a phishing attack.
Phishers usually use botnets to deliver because the banks (like Standard Bank) pay investigators to track them down (I would send a mail to and ask them what variants you should be looking for - not guaranteed response) - so you need to be looking for trojans/infections, not open relays. belongs to Standard Bank (checked it on the ZA registar, and they usually have SPF in place
(Received-SPF:       fail ( domain of does not designate as permitted sender) client-ip=;

Authentication-Results:; spf=hardfail ( domain of does not designate as permitted sender)

So there is NO WAY they would have any application that would be trying to send this out.

Definitely an infection.
Barry GillChief of StaffCommented:
lol, just checked the spf on and they have not set it... but their messages come from usually - they must have purchased the domain to prevent phishers from using it... I have sent them a mail rectify.
Alan HardistyCo-OwnerCommented:
You won't be an open relay - but you will be an authenticated relay.
I have seen this time and time again recently.  Probaly about 30 servers compromised in this way, including two clients and my own Exchange 2010 server!
My article will assist you in resolving the problem.
RickFerrAuthor Commented:
I have enabled Sender Filtering in ESM and added the sender's email address ( to the list of senders to block.  This seemed to resolve the problem for about a day and half.  The problem of the mail queue started up again.  But now when I look at the sender's email address in the message stuck in the mail queue they are "" and "".    I am getting a bunch of 7004 and 3015 events in app log.  Here are two samples:

This is an SMTP protocol error log for virtual server ID 1, connection #16. The remote host "", responded to the SMTP command "mail" with "553 5.3.0 flpd121 DNSBL:ATTRBL 521< >_is_blocked.__For_information_see_  ". The full command sent was "MAIL FROM:<>  ".  This will probably cause the connection to fail.

A non-delivery report with a status code of 5.3.0 was generated for recipient rfc822; (Message-ID <>).  
Causes: Exchange mistakenly attempted mail delivery to an incorrect MTA route.  

If feel like if I add the two new email addresses to the sender filter list that I am just applying a temporary fix.  How do I get to the root of where the spam is starting.  Should I look at the PCs on the network again.  I have already gone through and cleaned any spyware/viruses detected.
Alan HardistyCo-OwnerCommented:
Please download and install Vamsoft ORF 30 day trial from and set the software to log mode only.

Then stop the smtp service on your server.

Load up the Vamsoft logs, start the SMTP service and refresh the logs (F5).  Check the logs for the first entry with a sender that is not a sender on your domain and then cross reference the date / time to your security event log and just before the exact time in the Vamsoft logs, you should see a corresponding login event.

Check the username in the login event and then change the password for that account.  Restart the smtp service again and then keep refreshing the Vamsoft logs.

Hopefully the problem will be gone, but if not, repeat until it does stop.
RickFerrAuthor Commented:
Thank you. I did find that there was a user account named Admin that someone may have created at some point with a nonsecure password.  As soon as I reset the passwork on this account the bogus emails stopped being sent.
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