SBS2003 - SMTP Error 450 - Try again later (but only on 1 customer)

Hi.  I support multiple customers.  They have an employee that uses att.net for his e-mail at home.  E-Mails sent to him are delayed at least 5 hours, and sometimes never leave the queue.  The strange thing is that I do not have this problem sending to him from another customer sbs2003 machine.

here is the smtp log info:

2006-04-26 05:52:50 204.127.134.23 OutboundConnectionResponse SMTPSVC1 DELL01 - 25 - - 450+busy+-+please+try+later 0 0 27 0 31 SMTP - - - -
2006-04-26 05:52:50 204.127.134.23 OutboundConnectionCommand SMTPSVC1 DELL01 - 25 QUIT - - 0 0 4 0 46 SMTP - - - -
2006-04-26 05:52:50 12.102.240.23 OutboundConnectionResponse SMTPSVC1 DELL01 - 25 - - 450+busy+-+please+try+later 0 0 27 0 16 SMTP - - - -
2006-04-26 05:52:50 12.102.240.23 OutboundConnectionCommand SMTPSVC1 DELL01 - 25 QUIT - - 0 0 4 0 16 SMTP - - - -
2006-04-26 05:52:51 204.127.134.23 OutboundConnectionResponse SMTPSVC1 DELL01 - 25 - - 450+busy+-+please+try+later 0 0 27 0 15 SMTP - - - -
2006-04-26 05:52:51 204.127.134.23 OutboundConnectionCommand SMTPSVC1 DELL01 - 25 QUIT - - 0 0 4 0 31 SMTP - - - -
2006-04-26 05:52:51 12.102.240.23 OutboundConnectionResponse SMTPSVC1 DELL01 - 25 - - 220+worldnet.att.net+-+Maillennium+ESMTP/MULTIBOX+mtiwmxc14+#45 0 0 63 0 15 SMTP - - - -
2006-04-26 05:52:51 12.102.240.23 OutboundConnectionCommand SMTPSVC1 DELL01 - 25 EHLO - roilabels.com 0 0 4 0 15 SMTP - - - -
2006-04-26 05:52:51 12.102.240.23 OutboundConnectionResponse SMTPSVC1 DELL01 - 25 - - 250-worldnet.att.net 0 0 20 0 203 SMTP - - - -
2006-04-26 05:52:51 12.102.240.23 OutboundConnectionCommand SMTPSVC1 DELL01 - 25 QUIT - - 0 0 4 0 203 SMTP - - - -
2006-04-26 05:52:51 12.102.240.23 OutboundConnectionResponse SMTPSVC1 DELL01 - 25 - - 221+worldnet.att.net 0 0 20 0 218 SMTP - - - -

If I telnet gateway.att.net 25 using customer #1 sbs2003 machine, I get 450 - busy please try later

Same command from another customer, and they get the connection.

Emails from comcast and yahoo zip straight to the guy's e-mail address, and dnsstuff.com has a new e-mail tester that passes.

I am not using a smarthost on either machine, DNS straight through.

I have checked my DNS to verify all machines on network (including server) point to the SBS2003 server for DNS and that SBS2003 is forwarding to 2 DNS servers, which have the up to date info on the gateway2.att.net and gateway1.att.net

HELP!