Follow these steps to modify the registry and change Outlook's attachment security behavior.
1.Exit Outlook if it is running.
2.Click Start, and then click Run. Copy and paste (or type) the following command in the Open box, and then press ENTER:
regedit
3.Verify that the following registry key for your version of Outlook exists.
Microsoft Office Outlook 2007
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security
Microsoft Office Outlook 2003
HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security
Microsoft Outlook 2002
HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security
Microsoft Outlook 2000
HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Outlook\Security
If the registry key exists, go to step 5.
If the registry key does not exist, follow these steps to create it:
A.Locate, and then click the following registry key:
HKEY_CURRENT_USER\Software\Microsoft
B.Under Edit, click New, and then click Key.
C.Type Office, and then press ENTER.
D.Under Edit, click New, and then click Key.
For Outlook 2007, type 12.0, and then press ENTER.
For Outlook 2003, type 11.0, and then press ENTER.
For Outlook 2002, type 10.0, and then press ENTER.
For Outlook 2000, type 9.0, and then press ENTER.
E.Under Edit, click New, and then click Key.
F.Type Outlook, and then press ENTER.
G.Under Edit, click New, and then click Key.
H.Type Security, and then press ENTER.
4.Under Edit, click New, and then click String Value.
5.Copy and paste (or type) the following name for the new value:
Level1Remove
6.Press ENTER.
7.Right-click the new string value name, and then click Modify.
8.Type the file name extension of the file type that you want to open in Outlook. For example:
.exe
To specify multiple file types, use the following format:
.exe;.com
9.Click OK.
10.Exit Registry Editor.
11.Restart your computer.
When you start Outlook, you can open the file types that you specified in the registry.
source: http://support.microsoft.com/kb/829982
bacteria comment: You can insert any extension as long its not a virus.. :D
