RFC 2034 SMTP Service Extension for Returning Enhanced Error Codes

http://www.ietf.org/rfc/rfc2034.txt
This memo defines an extension to the SMTP service [RFC-821, RFC- 1869] whereby an SMTP server augments its responses with the enhanced mail system status codes defined in RFC 1893. These codes can then be used to provide more informative explanations of error conditions, especially in the context of the delivery status notifications format defined in RFC 1894.

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Diagnostic code: smtp;554 Service unavailable [ Reply ]
I am getting this message back on only one of my email friends. I have tried everything I know to fix the problem and have asked friends for their advice but nothing seems to be working. Below is the message I receive:
Your message cannot be delivered to the following recipients:

Recipient address: hshaw@vvuhsd.org
Reason: SMTP transmission failure has occurred
Diagnostic code: smtp;554 Service unavailable; Client host [vms046pub.verizon.net] blocked by dul.dnsbl.sorbs.net; Dynamic IP Addresses See: http://www.sorbs.net/lookup.shtml?71.105.124.248
Remote system: dns;barracuda.vvuhsd.org (TCP|206.46.252.46|61081|163.150.180.35|25)

Glen Godden [ ggodden ( at ) goddens dot net ], 2009-02-01 09:03:46 #

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