I am looking for guidance in setting-up an Exchange 2007 for colocation. Basically, I want to provide my own Hosted Exchange Services box for a few of my own domains and users. I am familiar with Exchange 2007 as an internal mail server, but I'm not finding much iinformation about configuring and hardening Exchange for the type of role I'm shooting for. Are there any good KB articles, whitepapers or online resources for this type of thing? Obviously people are doing it, because every time I Google it, I get a list of Hosted Exchange providers. It would just be cheaper for me to colocate my own server rather than pay the $9/mailbox/month that most places are charging (or more). Thanks!

If your not trying to sell it as a service, its just a matter of locking down address lists and email address policies so the right GAL's and addresses are given to the right users. If you are trying to sell as a service. Sign up for Service Provider LIcensing (SPLA) from M.S. That is where I got all the documentation on setting up for hosting including provisioning automation, etc.