Can't Send Msg's Exchange 2003 (2003 small business edition)

i just setup a exchange server and i can receive mail just fine but when any user tries to send a email msg (to anyone) we get the following msg.

There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
  < #5.5.0 smtp;550-5.7.1 [Extrnal ip address is here] The IP you're using to send email is not authorized > 

Could it be a problem with my ISP.. it is AT&T by the way..... I also tried to change the delivery settings in the SMTP virtual server and that didnt work .. What could this msg mean?
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It means your ISP is blocking outgoing port 25. Contact them to make sure.

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ncottonAuthor Commented:
That is what I was thinking. I will contact them when they are open for questions.. lol
BTW, just curious, do you have your DNS configured properly? Like do you have your MX record set in your DNS?
ncottonAuthor Commented:
Yeah I have a MX record.
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