Problems with undeliverable messages after an NDR attack

HI,
I have a client who's exhcange server was taken over as a relay server (an ndr attack). I have since closed the hole and cleaned up as best I can. I searched the RBL/black lists I knew of and made sure I was not on the lists. I have a reverse dns record with the isp. We are still experiencing undeliverable messages (see below) from multiple sources. Are these all isolated incidences that have to be cleared by each domain name or am I still on a block list somewhere? I've tried contacting these different companies, but so far I have been unable to get our emails unblocked. Do you have any suggestions????

From: System Administrator
Sent: Saturday, June 28, 2008 9:12 AM
To: Kelly King
Subject: Undeliverable: RE: Delivery Status Notification (Failure)
Your message did not reach some or all of the intended recipients.
      Subject:  RE:
      Sent:     6/28/2008 9:12 AM
The following recipient(s) could not be reached:
      Kelly King on 6/28/2008 9:12 AM
            You do not have permission to send to this recipient.  For assistance, contact your system administrator.
            <calrayinc.com #5.7.1 smtp;550 5.7.1 <kingfit@northnet.net>... H:MXB [72.1.16.26] Connection refused due to abuse. Please contact your E-mail provider.>
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_____________________________________________
From: System Administrator
Sent: Wednesday, July 02, 2008 8:19 AM
To: Tammy Timm
Subject: Undeliverable: RE: Ricoh Color Copier Copy Count
Your message did not reach some or all of the intended recipients.
      Subject:  RE: Ricoh Color Copier Copy Count
      Sent:     7/2/2008 8:18 AM
The following recipient(s) could not be reached:
      Tammy Nelson on 7/2/2008 8:19 AM
            You do not have permission to send to this recipient.  For assistance, contact your system administrator.
            <calrayinc.com #5.7.1 smtp;550 5.7.1 <tammy.nelson@oshkoshofficesystems.com>... H:MXB [72.1.16.26] Connection refused due to abuse. Please contact your E-mail provider.>
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----- Original Message -----
From: System Administrator
To: kitch@sparrowmedical.com <kitch@sparrowmedical.com>
Sent: Thu Jun 05 16:30:09 2008
Subject: Undeliverable: Re: quantum rad room
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