We started getting rejection/bounce back on email sent out of zohodesk.

typically we have SMTP from our domain into zohodesk eg support@example.com      
our mail respones go back out as example : support@example.zohodesk.com
These email bounce with error:
access to this mail system from sender4-op-o16.zoho.com [136.143.188.16] has been rejected due to the sending MTA's poor reputation. If you believe that this failure is in error, please notify the intended recipient via alternate means.

I am not sure what/how we need to change our configuration to not get spam blocked. 
I tried the help but its not clear if we should do something with the zohodesk email or if we need to route back through our own domain at example.com.