Evolution of Exchange CAS

                                         Exchange 2000/2003:

Didn’t have CAS servers but they were known by “Front End” servers

Internal clients connected with Outlook through MAPI directly to Mailbox servers (using MAPI over RPC)

External clients used the “Front End” as more of a proxy that could handle RPC over HTTP (for Outlook Anywhere), HTTPS (for Outlook Web Access, or OWA), POP/IMAP

                                         Exchange 2007:

Introduces the CAS role which is more than a proxy server but offloads a significant amount of the load that the mailbox servers typically handled

Internal MAPI clients still connect directly to the MB role

                                        Exchange 2010:

Introduces a new service (MSExchangeRPC) so that the CAS Role is “true” middle tier

In Exchange 2010, the CAS Role handles both external and internal connections to the Mailbox role (with the exception of Public Folder connections)

MAPI and directory connections are handled by the CAS server now, relieving a ton of load off the Mailbox server role, and ultimately increasing the number of concurrent connections to a Mailbox server (in 2007 we had 64K and now we have 250K)

Load balancing and CAS Array concerns
Securing CAS

                                        CAS Role Aspects:

  • Outlook Web App: Allows you to access email through a Web browser (including IE, Firefox, Safari and Chrome)
  • Exchange ActiveSync: Allows you to synchronize your data between your mobile device or smart phone and Exchange. There are varying levels of ActiveSync support in devices and one key security element is remote wipe, which is not available for all devices
  • Outlook Anywhere: Allows you to connect to your Exchange mailbox externally using Outlook (RPC over HTTP) without going through a VPN connection
  • POP/IMAP: Mail clients other than Outlook that connect with POP or IMAP are supported through the CAS role
  • Availability Service: Shows free/busy data to Outlook 2007/2010 users
  • AutodiscoverService: Helps Outlook clients and some mobile phones to automatically receive profile settings and locate Exchange services

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