Exchange 2010 Client Access Server (CAS)
Together with the Exchange 2010, Microsoft introduced a new Client Access Role server much better than the previous version released with the Exchange 2007. The Client Access Server role it is one of the five main roles existent on Exchange 2010. CAS role supports Outlook Web Access, Microsoft ActiveSync (and other ActiveSync clients previously not supported), POP3 client and IMAP clients. The Outlook Web Access functionality of the CAS 2010 it's a pretty powerful tool and its in direct competition with the normal Microsoft Outlook 2007-2010 clients. With a powerful interface and many newly introduced features, the new OWA its designed to cover the needs of most demanding users with many new features for organizing the e-mails, managing the phone, Junk Mail settings, full calendar access, password settings, out of office and many more functions that in the past were only available trough the Microsoft Outlook clients.
Beside the OWA, the new ActiveSync, with direct push technology, available on CAS server 2010 it's also fully compatible with iPhone and Blackberry which was quite problematic in the past and not fully functional. Client Access Server 2010 also offers connectivity for the different mail clients used within the organization and it is responsible for the mail-flow between the Exchange 2010 Mailbox server and this clients. The CAS 2010 role must be installed in each and every Active Directory site where a mailbox server it's installed and it also holds the Autodiscovery service configuration.
On the new CAS 2010 server role we have two new services, the RPC Client Access and Address Book services that are establishing the RPC endpoint for MAPI, NSPI and RFR client access. In this new configuration the Information Store (mailbox server) will only accept RPC endpoint requests from the CAS servers. Also on the Exchange 2010 the WebDav has been removed and any application that uses WebDav will have to be upgraded or replaced.
Whatever your reasons are for uninstalling the Client Access Server role, please make sure that other servers with the same Client Access Server role are available in your organization in order to ensure a continuous mail flow between your Mailbox Server and your client computers and devices. If you are planing to decommission your entire Exchange organization then there is no need to have any extra Client Access Servers installed and you can just uninstall the role safely.