E-mails being rejected by recipient domain (Zoho address)

E-mails being rejected by recipient domain (Zoho address)

I set up my Zoho account and it seemed to be working. I have sent and received a number of e-mails on the account. Recently I tried forwarding an important e-mail and I received the following error:

Delivery to the following recipient failed permanently:

      x

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain  x  by  mx.zoho.com . [x].

The error that the other server returned was:
554 5.2.3 MailPolicy violation Error delivering to mailboxes

Has anyone encountered this or does anyone know how to fix this?

Thanks!