Postfix relay and local delivery?

From: Kenneth Ratliff 
Background -

I currently run my mail setup with a Postfix/Dovecot pair.

I'm working on getting Exchange running on the internal network (not
interested in commentary about how horrible Exchange is, trust me, I know,
I'm still going to do it anyway...)

My goal is to have postfix at the edge, accepting mail for the domain and
running the various filtering, and then assuming it passes, kicking it
into Exchange for final delivery.

However, before I flip that switch, like a responsible and upstanding
solutions engineer, I want to actually test and make sure it works,
without losing email, or generating any bounce messages. To that end, my
question is thus: Is there a way to configure postfix to both, deliver
locally as it has been doing, while simultaneously also relaying the
incoming messages to another host? My Google-fu seems to be failing me on
this subject.