How to setup an Exchange 2010 CAS Array to load balance MAPI

Since Exchange 2010 CAS servers now handle all internal and external client traffic to Exchange mailbox servers including Outlook MAPI traffic, the need for a highly available CAS array is critical to your design.

CAS arrary

So how do you load balance MAPI traffic? I found a some useful bits of information to help out:

  1. Load balance your CAS servers in a CAS array by whatever method you choose – Both Hardware LB or Windows Network LB are supported load balancers
  2. Create a MAPI A record in your internal DNS infrastructure that resolves to the Virtual IP Address (VIP) of the CAS load balancing array.  The DNS entry, for example, could be
  3. Configure your load balancing array to load balance the MAPI RPC ports:
    1. TCP 135
    2. UDP/TCP 6005-65535; or set static ports
  4. Use the new-clientaccessarray cmdlet to create the CAS array object. Such as:

New-ClientAccessArray –Name “School CAS Array” –Fqdn “” –Site “Boulder”

More here.

5.  You need to revisit any Exchange databases that were created before the CAS array was created and set the rpcclientaccessserver property to match the newly created CAS array. Such as:

Set-MailboxDatabase DB1 -RpcClientAccessServer “”

For more on Exchange Server 2010 CAS visit here.


Categorised as: Exchange, Microsoft

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