We have two mail firewalls (Border Ware ) in the DMZ area, their ip addresses are and

To implement load balancing (mails to be delivered to both of them in equal ) on these mail firewalls, I have been advised to use NAT for these two private ip addresses ( and to two different (not one) public ip addresses.

Since we have not got two much public ip addresses, my suggestion was to use PAT (not NAT),,,but when I use PAT can a PIX implement load balancing ?