Exchange 2013 Client Access Coexistence with Exchange 2010

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 (proxyà 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 (proxyà 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.

Client à CAS2013 (proxyà CAS2010 à MBX2010



ActiveSync (EAS) (31:30)

Client à CAS2013 (proxyà CAS2010 à MBX2010



Exchange Web Services (EWS) (35:30)

EWS settings always come from autodiscover.

Client à CAS2013 (proxyà CAS2010 à MBX2010



Exchange 2013 Client Access Coexistence with Exchange 2007



I do a lot of coexistence migrations for customers. The following guide explains how Exchange 2013 Client Access coexists with Exchange 2007 during a long-term migration.



Greg Taylor had a fabulous session on Microsoft Exchange Server 2013 Client Access Server Role at 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



All client access services should point to the Exchange 2013 Client Access Server role (CAS2013). CAS2013 redirects to legacy.contoso.com for OWA and proxies everything else. Specific URLS are used if set, otherwise CAS2013 proxies.







Autodiscover (10:40)


Internal and external DNS must be configured to point to Exchange 2013 CAS.  MBX2013 delivers Exchange 2007 XML for the correct AD site.


Client à CAS2013 (proxyà MBX2013





Outlook Anywhere (OA) (20:00)



CAS 2007 must be enabled for Outlook Anywhere. If OA2007 authentication is already set to NTLM you’re set, but if you’re using Basic authentication:


CAS2007 – 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 CAS2007 à MBX2007





Outlook Web App (OWA) (25:50)



Set CAS 2007 ExternalUrl to legacy.contoso.com.  Make sure that legacy.contoso.com resolves to CAS2007 in internal and external DNS.


Client à CAS2013 (redirect)à CAS2007 (legacy.contoso.comà MBX2007





ActiveSync (33:15)


Convoluted path caused by limitations in CAS2007 code, but it works.


Client à CAS2013 (proxy)à MBX2013 (proxy)à CAS2007à MBX2007



Exchange Web Services (EWS) (36:15)

EWS settings always come from autodiscover.  If a mailbox is on 2007 has to get EWS from CAS2007. Set the CAS2007 InternalURL and ExternalURL to use https://legacy.contoso.com/EWS/Exchange.asmx

Client à CAS2007 (legacy.contoso.com)à MBX2007