After several calls with Microsoft, a ROSS, and several other engagements, we have the following configuration below.   

Goal

Each DAG (Exchange 2013, and 2010) has 4 members, two in each site.  Assume that the cluster resource is in the respective "active sites".  Public folders are on Exchange 2010/Legacy

Clients

Outlook 2007, cached and non cached mode and newer.  Some are on-network, some are off network 

New York Subnet: 10.10.15.x

  Autodiscover: autodiscover.contoso.com
  DAG Name: NYCDAG , No Cluster Administrative point

  RPC setting on all Exchange 2013 databases: NameOfA2013Server.contoso.com
  RPC setting on all Exchange 2010 databases: old2010RPC.contoso.com

  ClientAccessArray: old2010RPC.contoso.com 

  Internal URLs and External URLs for all Virtual Directories (2013 servers)
      https://NYCCAS.contoso.com/x  (x is OAB, EWS, OWA, 

Note- we did have an ambiguous namespace where Autodiscover URL, and the RPC name were the same.  This has been corrected.

    Public Folder server PF01:  OutlookAnywhere is enabled, and has a name of PublicFoldersNYC.contoso.com.  1:1 NAT available to outside

    Exchange 2010 CAS Array: OutlookAnywhere is enabled and has a name of Legacy2010.contoso.com.  1:1 NAT available to outside.

San Francisco: 10.5.5.X

  Autodiscover: autodiscover.contoso.com
  DAG Name: SFDAG  (stretched DAG with NYC).  No Cluster Administrative point

  Internal URLs and External URLs for all Virtual Directories
  https://SFCAS.contoso.com/xxx

  2010 Public folders, CAS not yet configured.

Is it strange that we have 3 OutlookAnywhere endpoints in the NYC site? What is the preferred configuration?

I would set the 2010 server OUtlook anywhere to the same hostnames as the 2013 servers so client connections go through the 2013 CAS

i tried that, but seem to have issues with proxying that.

What internal URLs need to be configured? Should I remove "external URLs from the 2010 servers?

Will Autodiscover issue the Outlook Anywhere endpoint based on where the mailbox is? (e.g. a 2010 user gets the 2010 endpoint?) 

What if a user has access to a 2013 mailbox, will OL access both endpoints?

Hi,

In order to support access for Outlook Anywhere clients whose mailboxes are on Exchange 2010, you will need to enable Outlook Anywhere on your legacy Client Access servers and enable NTLM in addition to basic authentication for the IIS Authentication Method.

Then the Exchange 2013 Client Access servers RPC proxy component sees the incoming connections, authenticates and chooses which server to route the request to (regardless of version), proxying the HTTP session to the endpoint

About Client Connectivity in an Coexistence Environment, I suggest you can refer to the below blog:

http://blogs.technet.com/b/exchange/archive/2014/03/12/client-connectivity-in-an-exchange-2013-coexistence-environment.aspx

Regards,

David 

• Edited by David Wang_Microsoft contingent staff 5 hours 47 minutes ago