Upgrading first CAS server to Update Rollup in mixed environment

Users trying access OWA in the mixed environment and getting "The mailbox you're trying to access isn't currently available. If the problem continues, contact your helpdesk."

In mixed Exchange environment (ie. OWA client access for Exchange 2007 users goes  Exchange 2010 CAS Servers -> Exchange 2007 CAS Servers -> Exchange 2007 User), Exchange 2010 server must have previous version of OWA in it’s OWA folder.

Upgrade Exchange 2007 CAS server to Update Rollup creates new folder of files (like UR12 for Exchange 2007 SP3 created the folder ‘8.3.342.1’) which did not exist on Exchange 2010 CAS servers.

That causes problems for Exchange 2007 users to login.

To fix – copy the folder to Exchange 2010 CAS Server OWA folder (from upgraded Exchange 2007 CAS Server OWA folder) and do iisreset on Exchange 2010 CAS server.

More here: http://exchangeserverpro.com/owa-error-mailbox-trying-access-not-currently-available/ (scroll down to the end).

Exchange Control Panel - not only Control Panel after all

When the user goes to Options/Change password in OWA (Exchange 2010), user gets redirected to https://yourmailserver.yourdomain.com/ecp...  Therefore 'ecp' is not for working as 'control panel' only.  (You have to make sure ecp is available from outside access if you configure OWA access through TMG or another reverse proxy device)