Exchange MTA to DMZ or NOT

Hi,

I have a ever going discussion with peers. We use to have an exchange server for our internal mail and a pop 3 on unix for internet mail. We are installing a new exchange server to get internet mail (No Outlook web access or mailboxes on this machine just IMS) and we are consern with security. Is it better to put the new exchange inside the firewall ad open only smtp port or put it in a DMZ open smtp to dmz and netbios and all other ports needed from dmz to the internal network. I amwilling to pay 500 points for a complete secure but fonctional Cisco PIX solution.