Mail server security

I'd like to set up my main machine as an e-mail server so I can have the e-mail address of my choosing. My question is: What kind of security precautions do I have to take in order to ensure that my computer is safe and secure?

Thanks!

Ensure that you run a firewall with only the appropriate ports open (depending upon your services offered 110/25 etc.) and that your server of choice is not set up as an open relay so that you don't make it on any blacklists. In your case, assuming that this is your first, do a lot of research prior to embarking on this endeavor.