OAB Never Downloads for Outlook 2007 Clients with Exchange 2007 on Server 2008

Update: This post gets a lot of traffic, but I want to be clear the first step here is no longer required. Simply perform the solution at the end of the post.

This one killed me today. Exchange 2007 SP1, with Rollup Update 6 on Server 2008. Everything working perfectly with one exception – the offline address book (OAB) never downloads from the file distribution point for Outlook 2007 clients. Works fine via public folders, but not web-based. No error, no timeout, no progress indicator, no login prompt, Outlook just looks like it’s endlessly trying to download the OAB. I double-checked all the URLs, flipped around SSL settings, but still couldn’t figure out why it wouldn’t download. I would have been happy to see an error so I had something to search on. There were actually 2 problems here that made the situation a real pain in the ass.

First – the same bug that affects Outlook Anywhere on Server 2008 apparently does a number on the OAB too. The solution is to turn off kernel-mode authentication in IIS. Run this command to fix that issue and you’re halfway there. I ran across some blog that mentioned Rollup Update 7 may include this change by default.


C:\Windows\system32\inetsrv\appcmd.exe set config /section:system.webServer/security/authentication/windowsAuthentication /useKernelMode:false

Second – I had enabled a redirect at the Default Web Site root to dump clients to the /owa folder gracefully using the Microsoft methodology at Technet. If you read the procedure you’ll notice setting the redirect at the root sets the same redirect on every single virtual directory. So, you need to go in to each virtual directory and undo the change you made for the root. This works fine, or appears to until your Outlook 2007 client tries to download the OAB and hangs forever.

I brightly plugged the URL to the OAB.XML file into IE and was greeted with a 500 – Internal Server Error message without an authentication prompt. That didn’t seem right. After some searching I realized the reason why Outlook hangs forever is that it tries to hit this URL, gets denied, uses some back-off logic, and tries again. I believe the back-off gets longer and longer each time it fails.

What happens is that when you disable that redirect for the OAB virtual directory IIS 7 generates a web.config file in the C:\Program Files\Microsoft\Exchange Server\ClientAccess\OAB folder. This seems logical, as it overrides the redirect at the root level, and is necessary. Unlike every other web.config that is generated in the other folders like Autodiscover and OWA, Authenticated Users do not have read access to the file. This is why Outlook and IE can’t even access the /OAB virtual directory.

The fix is pretty easy. Open the web.config in the OAB folder, and give Authenticated Users both the read and read and execute permissions. Run a iisreset /noforce on the CAS server to bounce IIS. Just for good measure, on the client side I wiped out the Outlook profile, and the contents of the %USERPROFILE%\Local Settings\Application Data\Microsoft\Outlook folder. Once I recreated the profile the OAB downloaded just fine. All in a day’s fun…