postfix smarthost to relay in same domain

[str tux]

Hello List,

In our domain I got an existing mail server (Domino Server) and I
setup another mail server using postfix. Due to some license issues
for Domino, I want to use the new postfix server in adding new mail
users - but still maintain delivery between the two.

I have no much problem since in Domino smarthost settings are available.

But I'm wondering, where such settings in postfix?

Please guide me accordingly.

Regards,
str