<clientdomain #5.5.0 smtp;550 Denied by policy: Sender is listed on DNS-based RBL> clientdomain is not blocked

Hi everyone,
I have a client who get the messange below when ever he try to send an e-mail to the anyone@ISPdomain. The client domain is NOT blocked by the ISPdomain.
Note that sometimes he can send the mail to anyone@ISPdomain, some other times he can't: no change in configuration.
sending e-mails to other domains is ok. The client faceing the problem only with some domains including ISPdomain.
His server is exchange 2000, not open relay, nothing is filterd, and all is fine.
Any ideas?

The e-mail:
From: System Administrator
Sent: Thursday, October 28, 2004 11:14 AM
To: xxxx@ISPDomain
Subject: Undeliverable: xxx

Your message did not reach some or all of the intended recipients.

      Subject:  xxx

      Sent:     10/28/2004 11:14 AM

The following recipient(s) could not be reached:

      xxxx@ISPdomain on 10/28/2004 11:14 AM

            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.

            <clientdomain #5.5.0 smtp;550 Denied by policy: Sender is listed on DNS-based RBL>
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The error message means that your clients domain has ended up on an RBL black list. The NDR should tell you which one, you then need to test your clients mail relay to make sure that it is not an open relay. You will also need to contact the owner of the RBL list and find out why your client has been blacklisted.

This happened to a subsidiary of my company, they were added to an RBL list because on the WHOIS record of the domain there was no email address listed for the domain contact. We contacted the RBL list owner and they took us off the list.
SalehdAuthor Commented:
I work at the ISPdomain. And the client mail server is not blocked by it!
However, can you provide me with more details about the second point you mentioned.
Does your domain use RBL lists? If so which one. The NDR indicates that mail from your client is being rejected due to them being on the RBL list used by your organisation.
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I wonder a bit about what you say in your 01:20 post, Salehd. As munichpostmans says, the indication is that the receiving server at ISPdomain rejects the message. Are you sure this is not the case?

There is of course a possibility that the receipient address is being forwarded from ISPdomain to some THIRDdomain, and the rejection happens there. The SMTP-log in client's Exchange Server can probably provide more details.

The text "...... Sender is listed on DNS-based RBL" leads me to guess that the source might be Spamhaus.org, the most widely used DNS-based blocking service. Details on http://www.spamhaus.org/sbl/index.lasso. You can also check your clients sending address here, and take appropriate action if it comes up as blocked. Maybe you should also do the same with ISPdomain's sending address.....

Regards from Norway
Leif Henriksen


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SalehdAuthor Commented:
Thanks for the answer Cerebellum, I found that the client IP address is on XBL on http://www.spamhaus.org/ which the ISPdomain e-mail server use to virify spam mail.
I am glad to see that you have resolved the problem, Salehd. However, I guess e maybe Munichpostman should receive the points as he was the first one to indicate the solution. Or maybe a split?
SalehdAuthor Commented:
How can I split it?
Splitting is desribed in http://www.experts-exchange.com/help.jsp#hi19

If you want to change the awarding in this case, first read http://www.experts-exchange.com/help.jsp#hi17

Leif H
SalehdAuthor Commented:
Thanks for answer Cerebellum.
Thanks also for you munichpostman, although I will not change the point to this question, I am very thanksfull for you both. Maybe next time I will Split the point :-)
I am getting the below mentioned error when I am trying to send mail to a person and all my other mails are going out to other people and other places.

The following recipient(s) could not be reached:

      priya@xyx.com on 10/15/2007 12:23 PM
            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <ZZZZ.com #5.5.0 smtp;550 Denied. S3>
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