Exchange 2010 Client Access Coexistence with Exchange 2013

The following guide explains how Exchange 2013 Client Access coexists with Exchange 2010 during a long-term migration.

Note: If you are migrating from Exchange 2007 please see my companion article.

Greg Taylor had a fabulous session on Microsoft Exchange Server 2013 Client Access Server Roleat TechEd 2013. I highly encourage you to watch it. For reference I've noted the time in the presentation that relates to each Exchange protocol below. So, off we go...

The Key to Enlightenment

CAS2013 proxies everything. Legacy namespace is not used. Specific URLS are used if set, but if a client comes to the wrong place CAS2013 will proxy to just "make it work". Making it work is better than making it efficient.

Autodiscover (8:40)

Internal and external DNS must be configured to point to Exchange 2013 CAS.

Client à CAS2013 (proxy) à CAS2010

Outlook Anywhere (OA) (19:17)

CAS 2010 must be enabled for Outlook Anywhere. If OA2010 authentication is already set to NTLM you're set, but if you're using Basic authentication:

CAS2010 - OA Client authentication: Basic / OA IIS authentication: Must include NTLM

Get-OutlookAnywhere -Server <server> | Set-OutlookAnywhere -ExternalClientAuthenticationMethod Basic -InternalClientAuthenticationMethod Basic -IISAuthenticationMethods NTLM

CAS2013 - OA Client authentication: Basic / OA IIS authentication: Basic

Get-OutlookAnywhere -Server <server> | Set-OutlookAnywhere -ExternalClientAuthenticationMethod Basic -InternalClientAuthenticationMethod Basic -IISAuthenticationMethods Basic

Client à CAS2013 (proxy) à CAS2010 à MBX2010

Outlook Web App (OWA) (23:00)

No legacy.contoso.com namespace used here. It's pure proxy. CAS2010 SP3+ allows silent proxy even if FBA is on CAS2010. 2013 CU2+ provides SSO with multiple Internet-facing namespaces.