Yes you can use both on same server, but not the same port. Only one program can use port 25 on a single computer.
In your instance i would set up another computer (perhaps even a VM) with IIS SMTP or hmailserver installed, and use it for your mass mail out.
I use two servers both with hmail on to send out mass email and keep regular mail flowing.
Thanks mattg and DooM. I want to make sure all mail goes out from one public IP which my PTR points to. Can I use multiple boxes with their own instance of hmailserver and direct all traffic out of the one server? I currently have two mail servers but only use one. I'd like to use them both but I'd prefer not to set up a new PTR going to the other mail server. I'll do that if I have to but is there a better way to do that?