smtp_bind_address

[Jerrale Gayle]

 I have smtp_bind_address set to the delegated ip for our mail server 
173.50.101.12; however this only limits incoming connections to that ip, 
along with our firewall; it USE to, on postfix, make postfix send out 
from that ip only. Now, postfix is sending out on the main ip of the 
mail server, 173.50.101.11, which is the backup DNS server's ip and 
causes mail to be rejected by those using our SPF record. I do NOT want 
to list the dns server's ip to be allowed to send mail, in our SPF. I 
have even tried changing smtp, in master.cf, to have -o 
smtp_bind_address=173.50.101.12.

 How can I make postfix use the ip it is suppose to, to send mail on?
I have also defined inet_interfaces=173.50.101.12