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Exchange says cannot deliver message because IP is blocked

I recently installed a new SBS 2003 R2 server at my company about 3 weeks ago.  Everything has been fine but today a user told me all emails to a particular user were being rejected with the error that is attached.  Does this mean my company's public IP has been blacklisted, is it a permissions issue, is it on AT&T's end, my ISP's end?  A little light would be helpful.  THanks!
FROM : System Administrator
SUBJECT :  Undeliverable:FW: TOMRI rent to TREHC
 
BODY OF MESSAGE (has been edited for privacy):
 
Your message did not reach some or all of the intended recipients.
 
Subject:	FW: TOMRI rent to TREHC
Sent:	10/9/2008 11:01 AM
 
The following recipient(s) could not be reached:
 
  XXXX@sbcglobal.net on 10/9/2008 11:01 AM
  The message cannot be delivered due to a configuration error on the server. Please contact your Administrator.
  <XXXX.com #5.3.0 smtp;553 5.3.0 flpi127 - m99H1wgD009159, DNSBL:521< MY.PUBLIC.IP.ADDRESS >_is_blocked.__For_information_see_http://att.net/blocks>

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jasdak
Asked:
jasdak
2 Solutions
 
Dan560Commented:
do you have reverse dns? check if you server has been blacklisted here
http://www.mxtoolbox.com/blacklists.aspx
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Exchange_GeekCommented:
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BertlingCommented:
hi there, you need to create a reverse DNS entry in your external DNS also make sure the FQDn on the SMTP virtual server is the name of the external mailserver A record.

see this and make sure you have done every thing: http://www.amset.info/exchange/dnsconfig.asp

also do you have a static IP address?
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jasdakAuthor Commented:
i will check that and be back with you. thank you
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Exchange_GeekCommented:
Sure, we are all waiting to hear from you.
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