The following are best practices from this chapter:
Use a front-end server in a DMZ firewall configuration for the most secure OWA client access from the Internet.
Use SSL encryption wherever possible for client access from the Internet.
Upgrade or replace all Exchange 2000 front-end servers before upgrading any back-end mailbox servers to Exchange Server 2003.
Disable any unnecessary services or protocols on a front-end server.
Use network load balancing to load-balance multiple front-end servers.
Replace, rather than upgrade, existing Exchange 2000 front-end servers to recover expensive Exchange Enterprise licenses.