If you want to learn how Microsoft IT used the features of Exchange 2007 Edge Transport role, check this out. Here is an official summary:
In deploying the Exchange 2007 based messaging protection solution, Microsoft IT used all messaging protection features of the Edge Transport server role and Forefront Security for Exchange Server to block, delete, reject, or quarantine unwanted messages. To further increase security, servers were hardened and audited for vulnerabilities to ensure readiness for Internet visibility. The many steps that Microsoft IT took to design a network environment, combined with the messaging protection features of Exchange Server 2007, resulted in greater flexibility, fewer false positives, and reduced TCO.