Can I enforce a specific Safe Senders list for the Junk E-mail Filter in Microsoft Office Outlook 2003 without allowing users to add addresses or domains to the list?
No, you can't prevent users from modifying the Safe Senders, Blocked Senders, or Safe Recipients list. Although you can use Group Policy Object (GPO) settings to cause Outlook to import one or more lists from a stored text file, users can still add their own entries to the lists. But you can use a GPO to mandate that Outlook import specific lists each time it starts.
An essential part of making this work is to obtain and install on each client machine the Outlook 2003 hotfix described in the Microsoft article "The JunkMailImportLists registry value may cause poor performance in Outlook 2003" (http://support.microsoft.com/?kbid=893057). As I explain in "Avoiding Performance Problems When Deploying a Safe Senders List," June 2005, InstantDoc ID 45976, the hotfix makes a key change in Outlook's operation to avoid performance problems when you use a GPO to force Outlook to import junk mail lists.
The next step is to make the necessary setting available to Group Policy Editor (GPE). You don't want to edit the original Outlk11.adm Administrative Template for Outlook 2003; if you do so, all changes will be lost when you overwrite that file with the new one from the next Office service pack.
Instead, you can create a new Administrative Template .adm file to hold settings that aren't in the Outlk11.adm file. Use Notepad or another text editor to create a file named ol2003extras.adm that contains the text shown in Listing 1. (You can download Listing 1 from the Exchange & Outlook Administrator Web site. Go to http://www.windowsitpro.com/microsoftexchangeoutlook, type 46661 in the InstantDoc ID text box, and click the 46661.zip hotlink.) Save that file to the default location for .adm files—the Winnt\inf (or Windows\inf) folder on your domain controller (DC). After saving the file, add it to GPE. Right-click the Administrative Templates node, choose Add/Remove, click Add, and select the ol2003extras.adm file. Click OK, click Open, then click Close to import the .adm file settings into GPE. You should be able to see your new setting in GPE and use it to turn on the import, as Figure 1 shows.
When this policy setting is in place for a user, each time Outlook starts it will import the junk lists whose paths you've set with the policy settings under Administrative Templates\Microsoft Office Outlook 2003\ToolsOptions\Preferences\Junk E-mail. By default, Outlook doesn't overwrite the existing junk mail lists when it performs the import. I think it's important to keep that default setting. Overwriting the users' list every time will probably just frustrate them and generate Help desk calls.
To learn more about using GPOs to enforce Outlook settings, see "Creating a Group Policy for Outlook 2002," August 2003, InstantDoc ID 39167.