reverse lookup failure error for a Mail sent to outside the domain.

Hi All,

Need your inputs . we are getting below error when we are sending mails to other domains.

Delivery has failed to these recipients or groups: myname@att.net Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept email from certain senders, or another restriction may be preventing delivery. The following organization rejected your message: al-ip4-mx-vip2.prodigy.net. ... We have a VIP created for our domain with IP 198.x.x. 141 with 2 servers load balancing under this. while sending mails it is using different NAT IP with server 10..74.x.54/198.x.x.53, please find diagram attached and let me know how to fix this issue

Diagnostic information for administrators: Generating server: inpgp04lvp.noam.fadv.net jonblack000@att.net al-ip4-mx-vip2.prodigy.net Remote Server returned ''