I've received numerous email from people describing a strange problem they've encountered with Microsoft Outlook 2007. Apparently, in some organizations, one or more users report that email messages disappear out of their Sent Items or Deleted Items folders. The messages later reappear.
When I experienced this problem, the circumstances surrounding the event prevented me from being able to perform any type of diagnosis. Even so, I wanted to offer my suggestions for diagnosing the issue.
In all of the cases of items disappearing from Microsoft Outlook 2007 folders and then reappearing, both the PCs and Outlook were configured identically across the organization. This is a big clue, because if all client machines are truly configured identically, and only one or two machines experience the problem, then the machine's configuration can be ruled out as a potential cause.
Initially, I thought latency might be to blame. For example, if the client machine contains a defective network card or if there are problems with the network cable that's connected to the client machine, then the machine could be performing an excessive number of retries while attempting to communicate with the Exchange server.
But this theory isn't completely viable since Microsoft Outlook 2007 uses cached mode by default. Therefore, all items in the Sent Items and Deleted Items folders are stored locally within the user's profile. When the user opens Outlook, this cached information is loaded immediately and Outlook attempts to connect to Exchange to download any new items or any changes to items that have been cached already.
If Outlook client-side caching is enabled, and I confirmed that it was in some cases, I think that the problem may be cache-related. I believe this because, in many of the reports, the user first noticed that the folders were empty immediately after opening Outlook. Therefore, the off-line cache, or some portion of it, is becoming corrupt. The items may eventually reappear because Exchange Server repopulates the cache.
This is just a theory, though, and I have no way to test it. I recommend that if a user is experiencing this issue, he should begin the diagnosis by disabling off-line caching.
To disable cached Exchange mode, choose the Account Settings command from Outlook's Tools menu. When the Account Settings properties sheet is displayed, go to the Email tab and double-click on the problematic mailbox.
This will cause Windows to display the Change Email Account dialog box. Deselect the Use Cached Exchange Mode box, click Next and then click Finish. Click Close to return to the main Microsoft Outlook screen.
I've been told that the problem of Microsoft Outlook email disappearing and then reappearing usually occurs intermittently. Therefore, I recommend running Outlook on the machine with cached Exchange mode disabled for a few weeks. This will give you the chance to determine if disabling the cache fixes the problem.
If the problem goes away, I recommend deleting the corresponding cache file and re-enabling Exchange Cache Mode. Deleting the cache file is safe because all of the user's data should still reside on the Exchange server. Deleting the cache file and then re-enabling Exchange caching forces Outlook to rebuild the cache from scratch.
The cache file is an .OST file stored within the user's profile directory. The actual file name varies from user to user, but there should only be one .OST file in the user's directory. The actual location of the offline cache also varies, depending on the version of Windows being used. In Windows Vista, the .OST file is stored in the C:\USERS\
About the author: Brien M. Posey, MCSE, is a five-time recipient of Microsoft's Most Valuable Professional award for his work with Exchange Server, Windows Server, Internet Information Services (IIS), and File Systems and Storage. Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal website at www.brienposey.com.
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This was first published in November 2008