Office 365 received the message that you specified. Unfortunately, we couldn't deliver the message to the recipient ({0}). ...

Office 365 received the message that you specified. Unfortunately, we couldn't deliver the message to the recipient ({0}). We couldn't deliver the message because the recipient domain doesn't have a valid MX record. We sent an email (non-delivery report) to the sender that gives the details about why the message couldn't be delivered.