| Separation of email server roles supports operational security for application and protocol services. The HTTP path to web sites is a proven convenience in requiring only a browser to access them, but is simultaneously a well known attack vector for people and applications that would attempt to gain unwelcome admittance to internal networks.
Web-based email applications, such as Exchange Outlook Web App (OWA), are classified as 'internal' or 'private' web servers. As with all web servers in the DoD, Internet-sourced email requests must be encrypted, authenticated, and proxied prior to permitting the transaction to access internally hosted email data. For email domains using Microsoft Exchange Client Access (CA) servers, Microsoft recommends and supports that all email CA servers reside inside enclaves (rather than a DMZ location) where firewalls would separate them from the other email servers. DoD PKI approved mechanisms for authentication are required for email access in the DoD. Multiple products exist that could meet the intent of this requirement, such as combination firewall and proxy servers, multi-tasking load balancers or shared authentication services for Internet-sourced traffic.