Is it blocked / blacklist by system ?

We received the auto message as below when sent out - 

This message was created automatically by mail delivery software. 
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. 

sales@keentop.com.hk , ERROR_CODE :500, ERROR_CODE :5.5.1 Command unrecognized: "" 

Received:from mail.zoho.com by mx.zohomail.com 
    with SMTP id 1478161369515211.9331461213909; Thu, 3 Nov 2016 01:22:49 -0700 (PDT) 
Message-ID:<15829488997.ee 3eea642187.8455088372758295032@kevinwebdesign.com > 
Date:Thu, 03 Nov 2016 16:22:49 +0800 
From:Tam Kevin < info@kevinwebdesign.com > 
User-Agent:Zoho Mail 
To:< sales@keentop.com.hk > 
Subject:回复 Fw: test by 0101 
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