If your running Exchange 2010 and utilize Outlook Anywhere, you may have users who complain that they cannot open an additional mailbox. When they go to expand the additional mailbox, they get the error “Cannot Expand the subfolder” or a similar error. The scenario is that you have two separate Active Directory sites, and you have outlook anywhere served out of each of them. For example:
User – Paul Ponzeka
Site – NewYork
OutlookAnywhere URL – outlookanywhere-NY.company.com
User – Jon Smith
Site – SanFrancisco
OutlookAnywhere URL – outlookanywhere-SF.company.com.
When you add Jon Smith as an additional mailbox to open in Paul Ponzeka’s exchange profile, you cannot open Jon Smith’s mailbox.
This is due to a change in behavior in Exchange 2010 SP2 RU3. The CAS servers now will try to force a user to connect to a CAS server that is in the local site of the mailbox your trying to connect to. You can see this in the RPC log:
2012-09-10T17:02:06.140Z,92,1,/o=Company/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=Paul Ponzeka72f,,OUTLOOK.EXE,14.0.4760.1000,Classic,,,ncacn_http,,DelegateLogon,1003 (rop::UnknownUser),00:00:00.0156005,"Logon: Delegate, /o=Company/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=John Smith in database DAG01-MDB12 last mounted on SF-MBX04.company.corp at 9/6/2012 2:45:10 AM, currently Mounted",RopHandler: Logon: [RopExecutionException] The client should use Outlook Anywhere and RpcClientAccess server from site SanFrancisco to access the mailbox.. Error code = UnknownUser
The import portion of the log is:
“The client should use Outlook Anywhere and RpcClientAccess server from site SanFrancisco to access the mailbox.. Error code = UnknownUser”
What is happening is the CAS server that Pauls mailbox connects to for Outlook Anywhere has determined that the San Francisco site has a CAS server that is better suited to handle the request for Matt Williams mailbox. However, since Paul is opening it as an additional mailbox, he cannot open the mailbox and the connection fails. The workaround is the create the following registry entry:
Create a DWORD entry named EnablePreferredSiteEnforcement and ensure the value is set to 0. Recycle the Microsoft Exchange RPC Access Service and this should fix it. The fix is described in the following KB article from Microsoft: