Unblock Attachments

Believe it or not but some people are actually creating and sending messages with attachments that will do your computer no good. Yes, you are correct; VIRUSES! There are a lot of file types in which a virus can reside. The most known are executables (programs) and scripts (automated processes). A filename consists out of 2 parts; a name and an extension. The extension is the part of the filename after the dot. For instance the filename document.doc. Document is the name part and doc is the extension part. The last part decides how the file opens. In our example a doc file will open with Microsoft Word.

At the moment there is a limited (but not a definite) list of file extensions that are known to be potential viruses. Outlook takes no changes and blocks these files whether or not it contains a virus because Outlook is not a virus scanner and therefore cannot determine whether the file is save or not. This is actually a good thing; even unknown viruses will be blocked this way! The downside of this is that occasionally you could receive a file that you know is clean but still can’t access. For instance; you receive a little (Flash) game or other program by e-mail.

This is the list of file types that are blocked by Outlook (clicke here for the latest list published by Microsoft)

Extension       File type
---------------------------------------------------
.ade            Microsoft Access project extension
.adp            Microsoft Access project
.asx            Windows Media Audio / Video
.bas            Microsoft Visual Basic class module
.bat            Batch file
.chm            Compiled HTML Help file
.cmd            Microsoft Windows NT Command script
.com            Microsoft MS-DOS program
.cpl            Control Panel extension
.crt            Security certificate
.exe            Program
.hlp            Help file
.hta            HTML program
.inf            Setup Information
.ins            Internet Naming Service
.isp            Internet Communication settings
.js             JScript file
.jse            Jscript Encoded Script file
.lnk            Shortcut
.mda            Microsoft Access add-in program
.mdb            Microsoft Access program
.mde            Microsoft Access MDE database
.mdt            Microsoft Access workgroup information�
.mdw            Microsoft Access workgroup information
.mdz            Microsoft Access wizard program
.msc            Microsoft Common Console document
.msi            Microsoft Windows Installer package
.msp            Microsoft Windows Installer patch
.mst            Microsoft Windows Installer transform; Microsoft Visual Test source file
.ops            Office XP settings
.pcd            Photo CD image; Microsoft Visual compiled script
.pif            Shortcut to MS-DOS program
.prf            Microsoft Outlook profile settings
.reg            Registration entries
.scf            Windows Explorer command
.scr            Screen saver
.sct            Windows Script Component
.shb            Shell Scrap object
.shs            Shell Scrap object
.url            Internet shortcut
.vb             VBScript file
.vbe            VBScript Encoded script file
.vbs            VBScript file
.wsc            Windows Script Component
.wsf            Windows Script file
.wsh            Windows Script Host Settings file

Before I tell you how you can still access those attachments you must realize that you are creating a security risk on your computer this way. A good practise is to send these files in a compressed (for instance zip or rar) format. This enables you to scan the file before unpacking and it will also take less inbox space and upload/download time!

Enabling to receive blocked attachments involves changing the registry. I strongly recommend to only edit the registry when you actually receive an attachment and there is no other way in getting that file again in a saver way (in compressed format) and you know for sure that the file is clean. Also change back the registry directly after you saved the attachment. It probably sounds paranoid but you’ll be hitting yourself if you get infected because you “opened the door and invited the virus” yourself.

Alright, here goes;

1. Make sure Outlook is closed.
2. Open your registry editor by opening the Run command and type regedit (regedt32 for Windows 2000)
3. Locate the following key
   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]
   Outlook 2007 [HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security]
4. Go to Edit-> New-> String Value and name the value Level1Remove (case sensitive!)
5. Double-click on the newly created value and enter the extension including the “dot” that you want to open in Outlook. For instance .exe
   If you need to enter more than one extension you’ll have to type separate them by a semicolon like this; .exe;.bat;.url
6. Press OK on the input box and close the registry editor
7. When you open Outlook the attachments which hold those extensions aren’t blocked by Outlook anymore.

To let Outlook block those extensions again follow the instructions again but instead of creating the Level1Remove value delete it.

If you are not comfortable with manually editing the registry or prefer easier access to block/unblock attachments you can also use OutlookTools (free).

Again; change back the registry directly after you saved the attachment or you’ll leave a door open for viruses!