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Open Relay using Exchange Server 2003

Posted on 2006-06-20
Medium Priority
Last Modified: 2010-03-06

   I recently the email below.  Does anyone have any ideas as to where else I should look to find an 'open relay', and how I could detect something like this.  I am using Exchange 2003, and I have verified that the Default Virtual SMTP Server only my two DNS servers listed under the Relay section.  I have also verified that the "Internet Mail SMTP Connector" and the "Every Domain" connector both have an * listed under 'Address Space' properties.  The checkbox "Allow messages to be relayed to these domains" is NOT checked.  

If I am using the exchange server only for my company's resources.  All the users with an email address are also registered in Active Directory.  Is it ok to uncheck the "Anonymous Access" and the "Basic Authentication" checkboxes under the Default Virtual SMTP Server's Access Tab, under "Authentication"

I have crossed out the ip address below for security reasons.  We are being charged with hosting an open relay, however I am pretty sure that our exchange server is secure.  We are also getting more junk mail than ever before...  Please help.


You are being contacted because Cogent Communications has received complaints concerning unsolicited email. The unsolicited mailings appear to be relayed through the unsecured mail server at IP address x.x.x.x.


Hosting an open relay mail server violates Cogent Communication?s Acceptable Use Policy. As a Cogent Communications customer you are expected to adhere our Acceptable Use Policies. Here is a summary of our AUP. To read in its entirety go to http://www.cogentco.com/htdocs/policy.php :


This Acceptable Use Policy applies to all persons and entities (collectively, "customers") using the products and services of Cogent Communications, Inc., ("Cogent") including Internet service. The policy is designed to protect the security, integrity, reliability, and privacy of both the Cogent network and the products and services Cogent offers to its customers. Cogent reserves the right to modify this policy at any time, effective immediately upon posting of the modification. Your use of Cogent's products and services constitutes your acceptance of the Acceptable Use Policy in effect at the time of your use. You are solely responsible for any and all acts and omissions that occur during or relating to your use of the service, and you agree not to engage in any unacceptable use of the service.


Please contact the appropriate sys admin and have him/her implement the proper configurations to secure the mail server.


Please respond once your system is secure therefore correcting this violation of Cogent Communication?s Acceptable Use Policy.




Cogent Communications, Inc.

Abuse Team


Question by:jeremyduj
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Accepted Solution

Sembee earned 2000 total points
ID: 16946091
Receiving junk email doesn't not have anything to do with being an open relay.
If the ISP has challenged you as being an open relay, then there are a couple of things to do.

1. Change your firewall configuration to block port 25 for all machines except the Exchange server. This will make any compromised systems inside your firewall show themselves.

2. Test the server. Looking at the settings isn't enough. I have instructions for testing the server on my web site here: http://www.amset.info/exchange/smtp-openrelay.asp

Whatever you do, don't use one of the web based test sites as that is the quickest way to get yourself listed - if you haven't already.


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