Yeah, I pointed the SMTP to the DNS Server, setup the relaying in the Exchange Server to allow the mail to relay from the web server (it's a different server), and it appears to be working fine... I sent some test emails, and monitored the bandwidth, and it seems to be going OK.
And since it is an intranet, it appears to be safe being behind the firewall and all... (but I am going to implement some security)
Thanks for the help all.