This is an issue that I run into daily and had a couple of Exchange hosting customers complain about. When you add an additional (or shared) mailbox to your Exchange account in Outlook, it does NOT cache any of the data like it does with your primary mailbox. It does case non-mail items, but switching back and forth between mailboxes can be very slow. Here is how to fix it…

This pertains to any Exchange version (as far as I know) and Outlook 2007 with SP2 or newer. If you have an older version of Outlook…upgrade! The instant search is worth it.

  1. Close Outlook.
  2. Click Start, click Run, type regedit, and then click OK.
  3. Locate and then right-click the following registry subkey:
    HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook
  4. Point to New, and then click Key.
  5. Type Cached Mode, and then press ENTER.
  6. Right-click Cached Mode, point to New, and then click DWORD Value.
  7. Type CacheOthersMail, and then press ENTER.
  8. Right-click CacheOthersMail, and then click Modify.
  9. In the Value data box, type 1 (decimal format), and then click OK.
  10. Open Outlook and watch as it begins to download and cache all of the additional mailbox data. Notice how the connection status now shows “Connected” rather than “Online” when viewing the other mailbox(es).
  11. Enjoy much quicker access between your mail folders!

I would like to cite two KB articles that helped me figure this out; KB955572 & KB936247. The first pertains to a hotfix for post SP1 Outlook, but has the settings we need. The second Tells us how to create the registry key that the first one assumes is present…it’s not. Even with Office SP2, the Cached Mode key is simply missing, so I put the two together to get it working.The second article mentions another DWORD value called “DownloadSharedFolders”. I presume it is enabled by default so adding it does not seem to make a difference.