You want to control the attachment types available to Outlook users on your servers.
If you want to change attachment blocking settings on a single computer to allow additional attachment types to be viewed, the process is quite straightforward. To change attachment blocking settings for Outlook on one computer, do the following:
Quit Outlook 2003.
Open the Registry Editor (regedit.exe).
Navigate to the following registry key: HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\.
If a subkey called Security exists, skip to step 7.
If not, select the key and choose New→ Key from the Edit menu; name the new key Security.
Select the Security key, then choose New→ String Value from the Edit menu.
Name the string value
Level1Remove key and choose
Enter the extensions of the file types you want to access through Outlook. You can type multiple extensions separated with semicolons, such as:
Quit the Registry Editor.
Restart Outlook 2003.
You can also use the Outlook Administrator Pack to apply attachment blocking settings to multiple computers. You do this by creating a public folder named Outlook Security Settings, then installing a custom form in it and using that form to edit the security settings you want applied to your Outlook clients. Settings you apply in this manner will override settings on individual client machines.
If you choose to use this method, the first step is ...