How Do I Unblock Email Attachments in Outlook?

By default, Outlook blocks certain attachments that it determines to be “unsafe” based on the extension. Certain extensions such as .url, .exe, .asp, and others can contain malicious code that will damage or erase your data. Microsoft and UAB do not recommend cutting this functionality off, as you increase the risk of being affected by viruses or trojans.

Start the registry editor by pressing the Start button, Run, typing regedit and pressing OK.
In Registry Editor, expand, in turn: HKEY_CURRENT_USER > Software > Microsoft > Office > 11.0* > Outlook

* (Office 2003. For Office XP, expand "10.0". For Outlook 2000, expand “9.0”)

Expand each entry by clicking on the boxed plus sign to its left. If that's a boxed minus sign, then it's already expanded.
Now click on the Security entry.
On Registry Editor's menu bar, select Edit > New > String Value.
Replace the default name of "New Value #1" with "Level1Remove".
Right-click on Level1Remove and select Modify.
Enter the list of file extensions that you want to gain access to. The list is semi-colon separated. For example if you wanted to allow access to both ".url" and ".doc" files, then you would enter ".url;.doc".
Exit Registry Editor, and you're done. You may need to restart Outlook if it was running while you were doing this.