Emails not accepted by bellsouth.net / SMTPDIAG Error 220

Emails to bellsouth.net timeout. Worked three weeks ago just fine - can't figure out whats the cause.  I have emailed bellsouth.net to see if they are blocking us.  This is not a firewall issue I'm sure of it.  If I try to telnet I get a 550 Blocked message as though I'm blacklisted.  But I don't appear blacklisted on any of the searches I've done.  Please let me know if there is more information you need.  This is a single domain with a single Exchange 2003 server.

HARDWARE
Windows Server 2003 with Exchange 2003 SP2

TESTS
Checked my llocal DNS server everything is fine.
Contacted my ISP regarding DNS and things look good there.  
Contacted my hosting company and my records look good there MX, A etc...
Checked and our domain isn't on a blacklist and reverse dns is working
Uninstalled Symantec Antivirus that was installed in the meantime in case that was the problem - didn't resolve anything

Ran SMTPDIAG and received the following:
SOA Serial Number Match: Passed
Both TCP and UDP queries succeeded. Local DNS test passed
Both TCP and UDP queries succeeded. Remote DNS test passed
Checking MX Servers listed for person@bellsouth.net
Connecting to gateway-f1.isp.att.net [204.127.217.16] on port 25.
Error: Expected "220".  Server is not accepting connections.
Failed to submit mail to gateway-f1.isp.att.net
Connecting to gateway-f2.ispatt.net [207.115.11.16] on port 25
Error: Expected "220".  Server is not accepting connections.
Failed to submit mail to gateway-f2.isp.att.net
hazenweberAsked:
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Michael_CookCommented:
I believe ATT (and several others) require you to have a reverse DNS entry  (rDNS)  for your mail server. So they can resolve the IP address back to you.

Speak to your ISP who can create this entry
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acc-techCommented:
Use smtpdiag with the /v switch.
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absremoteCommented:
Also looking for help. Several of my clients, who have a properly working DNS system have the same problem. Emails to bellsouth.net are not delivered.
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