The Evolution of CAS in Exchange Server versions
2 years ago
Originally Published: 2011-10-30
Article Number
000057981
Applies To
Exchange 2000/2003/2010

RSA Web Agent

Issue
The Evolution of CAS in Exchange Server versions

Resolution

Exchange 2000/2003 didn't have CAS servers but they had "Front End" servers. With "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), POP/IMAP


Exchange 2007 introduced 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


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