We have an exchange server 2003 and our IP address was blacklisted.

When I check the Queue folder in the exchange server root directory, there are tons of Delivery Status Notification (Delay/Failure) emails to be sent out. The email has from: postmaster@ourdomain.com and sent out to different email addresses.

When this happened before, I saw what the IP address (outside our network) in the current sessions that looks like the culprit. So I added it in the blacklist using connection filter in exchange server. This time, when I checked Current Sessions, there were no active connections. But there are still a lot of emails to be sent out from the Queue folder. I have disabled SMTP for now.

I've read in link that if I disable Allow Anonymous Access then I won't be able to receive incoming email from the internet. In the Relay Restrictions dialog, only the localhost computer is in the list. And I have "Allow all computers which successfully authenticate" checked.

How can I find out who is sending out the spam?

Sample email content:

This is an automatically generated Delivery Status Notification.

Delivery to the following recipients failed.



From: postmaster@ourdomain.com
To: info@dhs.gov
Date: Mon, 27 Jan 2014 22:34:47 -0800
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
X-DSNContext: 7ce717b1 - 1194 - 00000002 - 00000000
Message-ID: <xxxxxxxx@ourdomain.com>
Subject: Delivery Status Notification (Failure)

closed as off-topic by joeqwerty, TheCleaner, Dave M, Rob Moir, voretaq7 Feb 3 '14 at 21:44

This question appears to be off-topic. The users who voted to close gave these specific reasons:

  • "Questions must demonstrate a minimal understanding of the problem being solved. Try including attempted solutions, why they didn't work, and the expected results. See How can I ask better questions on Server Fault? for further guidance." – voretaq7
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  • 3
    How can I find out who is sending out the spam? Ask your employees if they're a piece of malware. When one of them says "yes," that's your spammer. – HopelessN00b Jan 28 '14 at 22:25
  • 7
    Well, that's even worse, then. Stop running an open email relay. – HopelessN00b Jan 28 '14 at 22:28
  • 1
    @HopelessN00b I have checked for open relay already and our server is not. I'm not really an expert on server admin. But what else could it possibly be? – John Ng Jan 28 '14 at 22:30
  • 2
    look at the bounces, and look at the auth log, If you allow Auth, it is quite possible one of your users has had their Auth Credentials stolen, and being abused. Or it could be that you are getting tons of incoming to invalid recipients. and exchange is accepting and the bouncing to the envelope sender so you are a blowback source. looking at the DSN might help – Doon Jan 28 '14 at 22:45
  • 5
    If you don't have a competent mail administrator, why are you running your own mail server? Please don't take this the wrong way, but, you should be blacklisted. – David Schwartz Jan 28 '14 at 23:15

"When this happened before, I saw what the IP address (outside our network) in the current sessions that looks like the culprit. So I added it in the blacklist using connection filter in exchange server."

So what you are saying is anyone on the internet that can find your mail server will be allowed to send mail through it, except for this one ip address that you've specifically blocked. This is horrible and the wrong way to run a mail server. You MUST disallow relaying by default, and selectively allow relaying only for your internal network and or trusted addresses.

If (big IF) as your comment says above, you are not an open relay, then how was that address sending through you previously? One of your authenticated sender accounts may be compromised, but you ought to see that in the logs.

  • I used mxtoolbox.com to check if our server is an open relay and it says that it's not. I'm not really sure what the proper setup for exchange server is. I will update my post for further description of our setup. – John Ng Jan 28 '14 at 22:38
  • 4
    @JohnNg "I'm not really sure what the proper setup for exchange server is." With respect, the correct solution to the problem, then, is to hire someone who is and ask them to ensure the system is properly configured. – Rob Moir Jan 28 '14 at 22:45
  • Sure, but this is more of a secondary email domain and we have the primary mail server hosted by a third party provider. I'm trying to maintain this mail server just so I can learn more about server admin. – John Ng Jan 28 '14 at 22:51
  • 4
    @JohnNg if all this is to you is an learning opportunity then this server absolutely and positively should not be connected to the internet. You're currently maintaining the IT equivalent of a public nuisance (en.wikipedia.org/wiki/Public_nuisance) for your own entertainment and you'll get a well deserved email blacklisting for your trouble. – Rob Moir Jan 28 '14 at 22:56
  • 2
    @JohnNg In addition to what RobM said, "learning" on an Exchange 2003 server is a waste of time. It's so old, out-of-date and incredibly different from the newer versions of Exchange that everything you learn on it is going to be worthless. May as well be riding a tricycle to learn how to drive. – HopelessN00b Jan 28 '14 at 23:07

It turned out to be a compromised account. One of the users (no longer actively using this email account) has been hacked and using that account to authenticate to the SMTP server. I found this out after enabling the authentication logs in the event viewer for MsExchange Transport. Thanks a lot to @Doon for the tip.

  • This is the trend lately in sending spam; it's a great way to send legit-looking mail and ride on your hard work establishing a reputation. – Falcon Momot Feb 3 '14 at 6:38

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