MTA load balanced for outgoing mails

[Mudasar]

Hi,

.................Zimbra .....................|........Firewall
....................MTA.......................|
@domain1.com--------------------|--> Public IP 1

@domain2.com--------------------|--> Public IP 2


We have some interesting requirement, We are running Zimbra 7 NE edition.
As above diagram we have 2 domains setup on a single server(MTA), this server has private IP and this IP is mapped on two different publilc IPs on firewall.
I have following question
1) is that possible that we can use separate Public IPs for each domain.

Mudasar