Has anyone seen this MTA error before?

[bill at horne.net (Bill Horne)]

I just tried to send an email to a new domain, but I got an error from the sending MTA at attbi.com. Has anyone encountered this before? 

All suggestions welcome. TIA.

Bill Horne

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A message (from <bill at horne.net>) was received at 10 Jun 2003 12:49:40 +0000.

The following addresses had delivery problems:

<will at billhorne.com>
	Permanent Failure: 553_sorry,_that_domain_isn't_in_my_list_of_allowed_rcpthosts_(#5.7.1)
	Delivery last attempted at Tue, 10 Jun 2003 12:49:40 -0000

------------------------------------------------------------------------

Reporting-MTA: dns; rwcrmhc13.attbi.com
Arrival-Date: 10 Jun 2003 12:49:40 +0000

Final-Recipient: rfc822; <will at billhorne.com>
Action: failed
Status: 5.0.0 553_sorry,_that_domain_isn't_in_my_list_of_allowed_rcpthosts_(#5.7.1)
Diagnostic-Code: smtp; Permanent Failure: Other undefined Status
Last-Attempt-Date: Tue, 10 Jun 2003 12:49:40 -0000