A message that you sent could not be delivered to one or more of its recipients

A message that you sent could not be delivered to one or more of its recipients

Hi, I have two mail boxes in one domain. One box is the default one. If somebody sends emails to the second one (office (at) domain (dot) com)  they receive a message cited in the topic. If I change MX records in my domain manager to the default, there is no such message and Zoho can receive mail via POP. But once I change MX records back to Zoho MX, I cannot receive mail again.