I will be updating this article to see if I can find a version where this did not occur.I am thinking either pre-CU7 or Pre-CU5 would be the place to find it.Next we renamed the folder containing the OAB files (the folder with a name that looks like a GUID).
CAS maintains a log of each request it handles in the log files, present in %Exchange Install Path%\Logging\Http Proxy\OAB\. Take a look at the video @ 31.31 minute and understand the Outlook connection process and then jump to using Test email auto configuration with Outlook.
Exchange 2016 OAB After running into this issue, I fired up my Exchange 2016 RTM lab and I was able to reproduce the issue with a good copy and a failed and suspended copy of the database where the OAB generating mailbox is located.
So this is not limited to Exchange 2013, but the architecture upon which it is based.
After we removed, we tested the OAB to see if this would make a difference. Although Microsoft touts that the address book can now reside in multiple locations (CU 7 ) and the generating mailbox can be replicated via a DAG: “This new infrastructure can also take advantage of the high availability architecture of Exchange 2013.
The OAB mailbox can be deployed on a mailbox database that has multiple copies, thereby mitigating a failure mode that occurred in previous releases.” Ironic in that if the OAB generating mailbox resides in a database that has a failed copy, then it could potentially lead to failed downloads.