Dual delivery - mail is not being seen in zoho mail

Dual delivery - mail is not being seen in zoho mail

We are piloting zoho mail and have setup dual delivery before deciding on the next steps.
The experience has not been good so far, we've set up using the below option
  • Email Routing: When you select Email Routing, all the emails will be routed to the destination servers, irrespective of whether the email accounts are present in Zoho or not. 
However the email does not seem to be stable e.g. I have not been seeing any email in zoho since 8th of Aug (only 1 or 2). But when I check the legacy destination mail server, there were many emails for the days since 8th of Aug. I don't seem to hear back anything from zoho mail support team, there were only 1 response who does not address the problem but explaining about the email routing which I already indicated in the email that I'm aware and that is how it is setup... having second thoughts about zoho now.