I have my Zimbra server up and running and I LOVE IT. The webmail access does everything I could ever ask for and more.

While the documentation does a good job in walking through setup, I'm looking for resources on how to protect my data on the box. Should I set up a proxy for it? (The box is currently in my DMZ). Is that a bad spot for it? Besides a firewall, what else should I consider?

What's a good place for me to start learning how to secure this box?