A good checklist to see if your Exchange 2007 is secure

Basically, i setup an Exchange 2007 for the first time and deployed it. Quit a change from 2003. Anyway, i had to make a receive connector because there is a guest on their network (non-domain as well) that receives her email via POP3, but needs to relay off of the exchange server. She up and running, and i followed a forum article to do this. Basically allowed the entire 192.168.1.0/24 range to relay off of the server with the anonymous users in the permissions group.

I did read somewhere that by default open relaying is not allowed on the outside, but i want a definitive answer as to how to check to see if external relay is turned off. Not only for this setup, but any other 07 servers i come across. I haven't been able to find anything, and nothing really pops up if you Google it.

As of now i got the Client, Default, and interalRelay receive connectors. I never touched the client and default ones. But one thing that does scare me is that the "anonymous users" group is in the permission group in the Default connector.

Any thoughts?

Thank you in advance