E-mails not being delivered

E-mails not being delivered

Hi,

All my emails to a certain domain are not being delivered. After three failed attempts they are not in the recipient's spam folder nor were they bouncing back. Only after sending to a 'yahoo.com' domain and cc'ing the two email addresses that were failing, then I got the following e-mail back from your servers:

------------------------------------------------------------------------------------------------
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. 


Person 1, ERROR_CODE :Wrong state! 
Person 2, ERROR_CODE :Wrong state! 


Received:from mail.zoho.com by mx.zohomail.com 
    with SMTP id 1453470451529784.1983189664641; Fri, 22 Jan 2016 05:47:31 -0800 (PST) 
Message-ID:<152699704e2.be59 39f1297496.7186688877798567659@ O URDOMAIN.COM > 
Date:Fri, 22 Jan 2016 15:47:30 +0200 
From: ME
User-Agent:Zoho Mail 
To:<XXXXXX @yahoo.com > 
Cc: Person 1 , Person 2 , 
    Person 3
Subject: SUBJECT
Content-Type:multipart/mixed; 
    boundary="----=_Part_699349_1065625570.1453470450949"
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I receive e-mails from that private domain but they never get any of mine since the past week. Please assist as this has halted all my official e-mails with a very important supplier. Thanks.