The activesync feature makes use of the authorization only mechanism to reverse proxy Active Sync connections. This lets you punch exterbal client activesync connections such as the iOS or Android client through to your internal exchange servers. The end result is that you get push mail clients to work without placing an exchagne server on your border or passing client traffic into your network. Junos Pulse client is a network layer vpn client(except for the Android version) that allows applicaitons direct access to your internal network.
