Applies to Exchange 2010 Sp1
Some users in Exchange 2010 DAG, cannot open outlook with the following error:
Cannot open your default e-mail folders. The file C:\users\deniz\… \deniz.ost is not an outlook data file (.ost).
If outlook cached mode is not set, outlook cannot connect either.
Other users in the same DAG don’t have any problems.
In addition to error above, delete and create outlook profile, and ost files did not work. Actually error message is misleading the problem is not caused by corrupted ost file or mailbox permission issue.
Databases in the DAG uses CAS array in the site. A CAS array contains the 3 CAS Servers that are load balanced with Network Load Balancing. Mistakenly one of CAS servers in the array, is not in Active Directory site where mailbox server and 2 other CAS servers reside in. Therefore, users who connect to problem CAS server cannnot access databases on mailbox server and outlook cannot connect. RpcClientAccessServer property is set to FQDN of the CAS server Array but one of the CAS servers in the CAS array is in different Active Directory site. This is a misconfiguration.
Using Active Directory Sites and services move the problematic CAS server IP to Active Directory site where mailbox server and 2 other CAS servers resides in. When Site membership is corrected and AD replicates then outlook users can connect.