Mail SMTP settings

I have a PHP 4.x install on an Apache server. I have a PHP application and a call to the mail function. I have 2 static IP's on the server and I have one web server and one instance of postfix for each IP to basically separate the two sites. The only issue I have right now is sending mail via PHP. I have tried to set the SMTP server and reply address via a php_value in my httpd.conf file and via the ini_set function for my site in question. Regardless of these setting mail is sent from the www user at my main site domain: Return-Path: <www@mail.wavefront.ca> Received: from mail.wavefront.ca ([unix socket]) by mail.wavefront.ca (Cyrus v2.2.12-OS X 10.4.0) with LMTPA; Fri, 02 Dec 2005 12:45:07 -0700 I've also tried the IMAP functions but also with no success. I basically want the mail to look as though it was from the other domain. Dan T