Postfix Add Header Question

[Marc Perkel]

I know some of you out there use Postfix and I have a quick question 
that is a little off topic so I will apologize in advance and beg 
forgiveness.

I was just wondering how in Postfix that someone could add a header 
indicating the IP address of the connecting host. I'm asking for someone 
I'm working with and I'm an Exim guy and this is trivial in Exim.

Thanks in advance.