Chances are, the receiving email server is accepting, but preventing the mailing from delivered to the inbox.
As long as the recipient is at a private/business domain, they can contact their IT team to white list Delivra's sending domain or IP range. White listing either of these on the email server will then allow mailings to be delivered.
Sending domain: ne16.com
IP range: 220.127.116.11/23 (141.193.208.[0-255] AND 141.193.209.[0-255])