cpanel mail configuration; i need to change the IP for outgoing mail server

Hi, I'm having issues with email on my cpanel server. My main IP, the hostname, is blocked by google mail from past bad domains that were hosted on my server. I've cleaned up all of the domains now but I cannot figure out how to setup the mail server to use the *dedicated* IP of a couple of domains on the server. I've tried the "tweak settings", turn on "use domains IP for mail" in exim.. But all mail is still going out on the main IP. I'm looking for someone who has faced and fixed this problem. This should be really simple, hop onto my box via SSH and setup a few things, etc. I look forward to your responses, Jason