I would like to put a word of caution before you start. Allowing executable extensions would give you more freedom; however, it is less security on the other hand. I would strongly recommend allowing unsafe attachments just for a specific email, which you are expecting the attachment from the person you know, and undoing it after downloading the attachments.

In this article, I’m going to show you how you can lower the security level and allowing a file from a known source sent you. There’s a article in Microsoft Help and Support about it in more detailed.

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.

Microsoft Outlook 2000:
HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Outlook\Security

Microsoft Outlook 2002:
HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security

Microsoft Office Outlook 2003:
HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security

Microsoft Office Outlook 2007:
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security

4. Backup before you start

5. Add a New String Value called “Level1Remove”