Programming - - By Craig Buckler

How to Unblock Unsafe Attachments in Microsoft Outlook

This article was written in 2010 and remains one of our most popular posts. If you’re keen to learn more about email systems, you may find this recent article on taking control of your inbox of great interest.

There’s a vast range of desktop and online email clients but it’s hard to beat Microsoft Outlook. The application has been around since 1997 and, despite a few dodgy decisions regarding HTML rendering, it’s still the email client of choice for me and many others.

Unfortunately, there’s an Outlook message web developers hate:

Outlook blocked access to the following potentially unsafe attachments…

Thanks Microsoft. I know why you’re blocking that JavaScript file, but I know what it is and I really, really want it.

Outlook doesn’t allow you to unblock unsafe attachments. Fortunately, there is a way to obtain the file and prevent the embarrassment of requesting a renamed version. Before we start…

tip: BIG REGISTRY WARNING!

We’re about to delve into the Windows registry. Please move along if you don’t know what the registry is or have never dabbled with it before. It’s a dangerous place — once false move and your PC will explode.

The fix will also reduce Outlook security settings. That’s not a problem for someone with reasonable IT knowledge, but it’s not for everyone.

Still here? OK, here’s what you do:

1. Close Outlook

2. Run regedit.exe
Navigate to:

HKEY_CURRENT_USERSoftwareMicrosoftOfficeXX.XOutlookSecurity

Where XX.X indicates your version of Outlook:

  • 14.0 for Microsoft Office 2010
  • 12.0 for Microsoft Office 2007
  • 11.0 for Microsoft Office 2003
  • 10.0 for Microsoft Office 2002
  • 9.0 for Microsoft Office 2000

3. Create a new value
Create a new string value key in that location named:

Level1Remove

4. Choose your ‘safe’ file types
Edit the key and enter a list of attachment extensions you want to unblock. Each should start with a period and be separated with a semi-colon. For example…

To unblock JavaScript files only, enter:

.js

To unblock JavaScript, VBScript, and exe files, enter:

.js;.vbs;.exe

Click OK to save the value then exit regedit.

5. Restart Outlook
The attachment should be magically unblocked. Try rebooting if that’s not the case.

Microsoft provide a useful support page with alternative options and configuration advice for those using Exchange Server.