The Outlook 2003/Exchange 2003 combination can be very potent, offering significant benefits for both users and mail and network administrators. On the user front, a down e-mail server doesn't become as much of a problem since the user's mail is stored locally and can continue to be accessed until an e-mail administrator can recover the mail system. From the perspective of a network or mail administrator, Outlook 2003 clients mean less stress on an Exchange server since clients can access their cached mailboxes. Further, network communications improvements in both products mean less bandwidth consumption. For all of these reasons—and more—Outlook 2003 in cached mode is a boon and should be used whenever possible.
Exchange 2003 Service Pack 2 adds the ability to block connections from Outlook clients that are not operating in cached mode. Simply put, you need to make a change to the Active Directory object for each user you want to subject to this limitation.
The unfortunate part is that this process isn't super-easy and involves the use of a tool called ADModify.NET. You could also use ADSI Edit, included in the Windows server support tools, but, using the ADSI Edit method, you would need to make an individual change to every user object in your organization. ADModify.NET is a tool that allows bulk changes to Active Directory objects. The latest version includes the ability to make the changes to the fields that were introduced by Exchange 2003 SP2. Download ADModify.NET from here.
Installation of ADModify.net consists of extracting the contents of the downloaded zip file to a location on your server's hard drive. Execute the program by double-clicking on the ADModify.exe icon.
Once you start ADModify, on the opening screen, choose the Modify Attributes option. In the Domain List field, click the drop down button and select your domain. Next, from the Domain Controller List field, click the drop down button and choose the domain controller you want to use. In the Show Only field, limit yourself to just viewing User account since these are the AD objects you need to modify. Click the big green Go button (it's an arrow in a green box).
Now, you need to individually select the users you want to modify and click the Add to List button at the bottom of the ADModify window. Or, if you want to add all of the users in a particular OU, select that OU and choose the Add to List button. When you're done adding users, click the Next button.
On the next screen, choose the Exchange Features tab and, on this tab, choose the checkbox labeled "Enable Cached Mode MAPI Clients Only." Clock the Go! button when you're done. Due to caching, it can take quite some time before you changes to effect. But, once they do, modified users using non-caching clients will no longer be able to log into your Exchange system.
The standard caveats apply: Be careful when making mass changes to your network. Remember also that this tip works only with Outlook 2003 and Exchange 2003 SP2.