Securing Outlook Web Access (OWA) » DenyAll Security Blog

Running an Outlook server takes some expertise, but it takes just a bit more to secure it.  In this article, it shows some good methods to secure the server.  Some are simple , such as, encrypting all connections, but some are like using high end application firewalls with features such as grammatical analyzation and suspicious user tracking and mitigation. 

http://www.denyall.com/securityblog/securing-outlook-web-access/