AT&T DNS Block - Suggestions to fix this?

We are having a SBS 2003 server running at out office with several client workstations. Everything was working fine since a year but yesterday suddenly few of our users started getting couple of DNS Blocks from AT&T with the following message:

“The message cannot be delivered due to a configuration error on the server. Please contact your Administrator.
<lifetime-media.com #5.3.0 smtp;553 5.3.0 nlpi090 - m8QG9RbC031621, DNSBL:521< IP ADDRESS
>_is_blocked.__For_information_see_http://att.net/blocks>”

The setup is on Static IP, then what could be the problem? Any ideas?

Due to some security reasons, AT&T puts some users on their Blacklist. I’m not sure but you guys might have done something wrong OR by mistake AT&T might have put you in Blacklist which resulted in this problem.

You should try contacting AT&T for the same. They will help you out for sure.

You are right CoYoTeA but not completely. Actually they might have not put them on Blacklist but many times ATT blocks inbound port 25 and I guess this has happened because they are using inbound email and this company does not have a business class DSL account. You guys should look in for this.

Well I found an Article in ATT knowledge base which describes exactly your problem. You should check out the same, I’m sure it will help you. Here it is: http://worldnet.att.net/general-info/bls_info/521.html