Exchange 2007 550 5.1.1 User unknown

Hi,

I have a user his email gets bounds back.

xxx@xxx.com.au
The recipient's e-mail address was not found in the recipient's e-mail system. Microsoft Exchange will not try to redeliver this message for you. Please check the e-mail address and try resending this message, or provide the following diagnostic text to your system administrator.

The following organization rejected your message: mail.shareplate.biz.

Diagnostic information for administrators:

Generating server: polonium.mailguard.com.au

xxx@xxx.com.au
mail.shareplate.biz #<mail.shareplate.biz #5.1.1 smtp; 550 5.1.1 User unknown> #SMTP#


Could someone please explain how to troubleshoot this issue?
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suriyaehnopCommented:
You send the email to xxx@xxx.com.au which is the mailbox suppose to be available at mail.shareplate.biz.

The following organization rejected your message: mail.shareplate.biz.

Based on message "The recipient's e-mail address was not found in the recipient's e-mail system", you have to check with administrator at mail.shareplate.biz to identify whether:

1. That recipient's mailbox still available
2. Does the user had changed their SMTP email address

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