As many of you probably know Exchange Server 2010's new CAS, Client Access Server, will be what the name says : the endpoint of ALL client connections.
This is true for all kind of connections including Mapi, OWA, ActiveSync, Pop3, Imap, Outlook Anywhere and even .... Entourage. There is only one connection that is still being made directly to the Store and it is the Public Folder connection.
This will, of course, change the recommendations made when deploying CAS and Mailbox servers :
MAILBOX is now recommended to have 8 Cores and 8 Gb of RAM but it will depend on the size of your Organization (as always ).
CAS is now recommended to have 8 Cores and 8 Gb of RAM. Ideally 2 Gb of RAM per core or 16 Gb of RAM in total.
Why this change ?
Well there are a lot of improvements that have been done such as the failover of mailbox servers where Outlook clients will have no more than thirty seconds delay, as opposite to a lot more than one minute in Exchange 2007.
When you perform a Move-Mailbox it will be done without almost no disruption on the client side, meaning that you will still be able to use Outlook or OWA regularly. After the move is done Outlook will simply point to the new Mailbox Server. Quite nice, hum ?
This will also ease the code and cpu needed for operations by the Store itself, since a lot of the heavy workload is moving to the CAS now.
Note: Mapi on the middle-tier is the common name and there are no guarantees that it will remain with this name in the final product release.