Sender based outgoing IP selection

[Attila Nagy]

Hello,

I have to route e-mails coming from different IP addresses to the world 
(no single smarthost, the target can be anything) with different source IPs.

So a mail coming in on 1.1.1.1 should go out with the source address of 
2.2.2.2 and another coming in on 3.3.3.3 should go out from 4.4.4.4.
Postfix listens on 1.1.1.1 and 3.3.3.3 and the machine has also the 
addresses of 2.2.2.2 and 4.4.4.4 of course.

Am I right when I think this can only be done correctly with two postfix 
instances?

Thanks,