Cannot open attachments in Microsoft Outlook - How to Customize Attachment Security Behavior?

Outlook includes a feature that blocks attachments that are considered unsafe. If you receive an e-mail message that contains an attachment that contains one of the file types that are considered unsafe, you may receive the following message:
Outlook blocked access to the following potentially unsafe attachments: [......]
Although Outlook blocks access to the attachment, the attachment still exists in the e-mail message.This security feature provides an additional level of protection against malicious e-mail messages.
Use one of the following methods to open an attachment that was blocked in Outlook:
• Request that the sender post or save the attachment to a file share and then send you the link to that file share.
• Request that the sender use a file compression utility that changes the file name extension. For a list of third party compression products.
• Request that the sender rename the file name extension and then resend the attachment to you. After you receive the renamed attachment, you can rename the file with the original file name extension.
If the previously recommended methods do not meet your requirements, use one of the following methods:
• If you are in a Microsoft Exchange environment and your administrator has configured the Outlook Security
settings, ask the administrator to modify the security settings for your mailbox.
• If you are not in an Exchange environment, modify the Windows Registry to customize the attachment.

Warning: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Use Registry Editor at your own risk.

You can modify the attachment security behavior in Outlook if you are using Outlook in one of the following scenarios:
• You are not using Outlook in an Exchange environment.
• In an Exchange environment, the administrator has not configured the Outlook Security settings to disallow changes to the attachment security behavior.
In these scenarios, follow these steps to modify the attachment security behavior in Outlook by making a modification to the registry.
How to Customize Attachment Security Behavior
Important Before you can customize the attachment security behavior in Outlook, you must first apply either Office Service Pack 2 or Service Pack 3.
1. Quit Outlook if it is running.
2. Click Start , and then click Run.
3. In the Open box, type regedit, and then click OK.
4. Verify that the following registry key for your version of Outlook exists. If it does, go to step5.
Outlook 2000
HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Outlook\Security
Outlook 2002
HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security
Outlook 2003
HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security
If the registry key does not exist, create it. To create the registry key, locate and then click the following
registry key:
HKEY_CURRENT_USER\Software\Microsoft
a. Click the Edit menu, click New, and then click Key.
b. Type Office , and then press ENTER.
c. Click the Edit menu, click New, and then click Key.
d. Type 11.0, and then press ENTER.
Note: This is the correct name if you are using Outlook 2003. If you are using Outlook 2000 or Outlook 2002, you will need to type "9.0" or "10.0", respectively.
e. Click the Edit menu, click New, and then click Key.
f. Type Outlook, and then press ENTER.
g. Click the Edit menu, click New, and then click Key.
h. Type Security, and then press ENTER.
5. Click the Edit menu, click New, and then click String Value.
6. Type the following name for the new value:Level1Remove
7. Press ENTER.
8. Right-click the new string value name, and then click Modify.
9. 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
10. Click OK.
11. Quit Registry Editor.
12. Restart your computer.
When you start Outlook, you can open the file types that you specified in the registry.