Unknown Address Error 550 - 5.2.1 Message Rejected

  • From: joed@xxxxxxxxxxxxx
  • To: exchangelist@xxxxxxxxxxxxx
  • Date: Thu, 7 Apr 2005 16:57:14 -0600

We have an Exchange 2000 Server within our company.  Our users have
Outlook 2000 on thier PCs.  Someone tried to sending me an email with a
file attachment.  I was not able to receive the email with the attachment.
 The sender instead received a message in their email:

Subject: "Delivery Status Notification (Failure)" with the following

The following message to <email address> was undeliverable.  The reason for 
this problem:
5.1.0 - Unknown address error 550 - '5.2.1 Message rejected.'

Any ideas of what would cause this or where to start troubleshooting?



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