Error sending email

Hi,

Suddenly we receive this error for one of the receipient

us2.mx.mailhostbox.com rejected your message to the following e-mail addresses:

us2.mx.mailhostbox.com gave this error: Service currently unavailable Please seehttp://support.mailhostbox.com/email-administrators-guide/error-codes for explanation of the problem.

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Reporting-MTA: dns;exch.xxxxxxxxxx.my
Received-From-MTA: dns;HRPC
Arrival-Date: Mon, 6 Jul 2015 05:55:08 +0000

Final-Recipient: rfc822;liyana@xxxxx.net
Action: failed
Status: 5.3.2
Diagnostic-Code: smtp;550-5.3.2 Service currently unavailable
 550 5.3.2 Please see http://support.mailhostbox.com/email-administrators-guide/error-codes for explanation of the problem.
Remote-MTA: dns;us2.mx.mailhostbox.com

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knizam