What is the reason for the mail forward failure suddenly from zoho.com to codemantra.com?

As per our knowledge, our mail communication with microsoft.com/Office365.com Cloud Exchange Services always be online and have no chance of disconnection or host not reachable in any manner.

All the emails forwarded from zoho to codemantra.com more important to us. We can't go back to the client or customer for requesting the email which was failed to reach us.

From: mailer-daemon@mail.zoho.com [mailto:mailer-daemon@mail.zoho.com]

Sent: 01 June 2016 11:07 PM

To: typesetting@crccollab.com

Subject: Mail Forward Failure

 

The following message could not be forwarded to nickladuca@codemantra.com for typesetting@crccollab.com

 

Technical details of the failure:

, Host not reachable.

 

----- Transcript of session follows ----- 

 

 Return-Path:<crc_projectmanager@mtcstm.com>

 Received:from mail918.opentransfer.com (mail918.opentransfer.com [98.130.1.193]) by mx.zohomail.com

                with SMTP id 1464802594061959.0156670526101; Wed, 1 Jun 2016 10:36:34 -0700 (PDT)  Message-ID:<017f01d1bc2c$20471f90$60d55eb0$@mtcstm.com>

 Date:Thu, 2 Jun 2016 01:36:25 +0800

 From:"CRC Project Manager" <crc_projectmanager@mtcstm.com>  To:"'CRC Typesetting'" <typesetting@crccollab.com>

 Subject:RE: K26594 Index

 Content-Type:multipart/related;

                boundary="----=_NextPart_000_0180_01D1BC6F.2E6E7E40"

 

P.S: Please note that your email forwarding will be disabled if there are too many failures.