Unblock Outlook attachment client-side

There's a pretty long list of file types that Outlook blocks. The recipient can ask the sender to re-send the blocked attachment inside a ZIP file or with a different extension (like .txt or .pdf). You can also climb into the registry editor to access a blocked attachment:

HKEY_CURRENT_USER\Software\Microsoft\Office\[version]\Outlook\Security

Make a string named "Level1Remove" containing the extensions to unblock (e.g. ".exe;.bat").

Credit(?) to Microsoft.