A few people have asked in the past what CAS Proxying is. It comes in to play when you talk about Enterprise Vault Outlook Web Access components, specifically for Exchange 2007 and Exchange 2010. Exchange 2003 doesn’t have a concept of CAS Proxying (it was all in the world of front-end and back-end servers, if you can remember back that far).
What it is : It is the process of Exchange 2007 (or Exchange 2010) in proxying the request for Outlook Web Access to the “best” Client Access Server. To do this, an internet facing CAS will lookup the users Active Directory attributes, and coupled with the knowledge of the Exchange server topology will try to use a CAS in the users site.
There is a nice flow chart, and a bunch of useful information on the Exchange Team Blog :
The support for CAS Proxying has been around since Enterprise Vault first supported Exchange 2007 – but there has been a number of fixes added in the “early days”. (So use the latest version of EV OWA Addins)
There are some interesting pieces of the setup. They’re described in this technote :