SMTP in DMZ

Hello,
 
If a site does not receive much email, is it still a good idea to use a
separate SMTP machine to redirect mail to the Exchange server
Located back behind the internal firewall?  
 
What I really want to is active SMTP on my IIS machine in the DMZ and
get rid of my other machine that is just forwarding the message.
I have another need for my forwarding SMTP machine and can't afford to
leave it sit just as a forwarder.
 
Any thoughts and ideas are appreciated!
 
Thank you,
 
Joseph

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