Outlook 2007 – opening additional mailboxes is slow over a WAN link

By default, outlook 2007 will not cache an additional mailbox. Whilst on a quick LAN, this may not pose a problem, but if you are opening additional mailboxes over a slow WAN medium (such as satellite), this may cause outlook to go “Not responding”  or take quite a while to look through the mailboxes folders.

To resolve this issue, you need to do one of the following:

1. Pre Outlook Sp2 – download a hotfix + add a registry hack
2. Post Outlook Sp2 – add a registry hack

For the official word on the registry hack + additional instructions can be found here http://support.microsoft.com/kb/955572/

In short, this is what you need to do:

1. Ensure SP2 is installed
2. Locate and then click to select the following registry key: HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Cached Mode (if it doesn’t exist, create it)
3. Right-click CacheOthersMail, and then click Modify.
4. Type 1 in the Value data box, and then click OK.
5. (if it doesn’t exist, right click on Cached Mode and create a new DWORD – 32bit)
6. Exit Registry Editor.
7. In Outlook, On the Tools menu, click Account Settings.
8. Click the Email tab, click to select the Exchange account, and then click Change.
9. Click More Settings.
10. Click the Advanced tab, click to select the Download shared folders (excludes mail folders) check box, and then click OK.
11. Disable headers. To do this, follow these steps:
12. On the File menu, and then click Cached Exchange Mode.
13. Click to clear the following options:
- Download Headers and then Full Items
- Download Headers
- On Slow Connections Download Only Headers
(I couldn’t locate the above, so down on the bottom right hand corner of the screen I disabled “on slow connections download only headers” and I selected download full items)
- Close and re-open outlook

As a sanity check, if you want to confirm that the additional mailbox is being cached.. then go to where the OST is stored and confirm that it is growing in size (may need to close/reopen outlook).

References:

1. http://communified.net/archive/2009/05/08/caching-shared-additional-mailboxes-in-outlook-2007.aspx
2. http://support.microsoft.com/kb/955572/
3. http://technet.microsoft.com/en-us/library/cc179067.aspx
4. http://www.edwardsd.co.uk/work/blog/2010/07/08/outlook-2007-cached-mode/

A word of warning… If you enable caching of this additional mailbox, your local OST file will begin to grow.