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 chances 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 safe 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.

Blocked Attachments
Outlook informs you about any blocked attachments in the message header

Unblocking procedure

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 practice 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!

To enable receive blocked attachments involves changing the registry. I strongly recommend to only edit the registry when you actually receive a blocked attachment and there is no other way in getting that file again in a safer 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).
    In Windows Vista and Windows 7, you can also directly type regedit in the Start Menu’s Search box.
    In Windows 8, you can directly type regedit when you open the Start Screen, a search box will automatically appear when you start typing.
  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]
    • Outlook 2010
      [HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security]
    • Outlook 2013
      [HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\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 now 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).

Unblock attachments with OutlookTools
Easily unblock (and then block again) attachments with OutlookTools.

Again; change back the registry directly after you saved the attachment or you’ll leave a door open for infecting your computer with a virus!

List of blocked attachments

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

Extension File type description
.ade Access Project Extension (Microsoft)
.adp Access Project (Microsoft)
.app Executable Application
.asp Active Server Page
.bas BASIC Source Code
.bat Batch Processing
.cer Internet Security Certificate File
.chm Compiled HTML Help
.cmd DOS CP/M Command File, Command File for Windows NT
.cnt Help file index
.com Command
.cpl Windows Control Panel Extension (Microsoft)
.crt Certificate File
.csh csh Script
.der DER Encoded X509 Certificate File
.exe Executable File
.fxp FoxPro Compiled Source (Microsoft)
.gadget Windows Vista gadget
.grp Windows program group file
.hlp Windows Help File
.hpj Project file used to create Windows Help File
.hta Hypertext Application
.inf Information or Setup File
.ins IIS Internet Communications Settings (Microsoft)
.isp IIS Internet Service Provider Settings (Microsoft)
.jar JAVA archive file
.its Internet Document Set, Internet Translation
.jndi Java Naming and Directory Interface
.jnlp Java Network Launching Protocol
.js JavaScript Source Code
.jse JScript Encoded Script File
.ksh UNIX Shell Script
.lnk Windows Shortcut File
.mad Access Module Shortcut (Microsoft)
.maf Access (Microsoft)
.mag Access Diagram Shortcut (Microsoft)
.mam Access Macro Shortcut (Microsoft)
.maq Access Query Shortcut (Microsoft)
.mar Access Report Shortcut (Microsoft)
.mas Access Stored Procedures (Microsoft)
.mat Access Table Shortcut (Microsoft)
.mau Media Attachment Unit
.mav Access View Shortcut (Microsoft)
.maw Access Data Access Page (Microsoft)
.mcf Manifest configuration file
.mda Access Add-in (Microsoft), MDA Access 2 Workgroup (Microsoft)
.mdb Access Application (Microsoft), MDB Access Database (Microsoft)
.mde Access MDE Database File (Microsoft)
.mdt Access Add-in Data (Microsoft)
.mdw Access Workgroup Information (Microsoft)
.mdz Access Wizard Template (Microsoft)
.msc Microsoft Management Console Snap-in Control File (Microsoft)
.msh Microsoft Shell
.msh1 Microsoft Shell
.msh2 Microsoft Shell
.mshxml Microsoft Shell
.msh1xml Microsoft Shell
.msh2xml Microsoft Shell
.msi Windows Installer File (Microsoft)
.msp Windows Installer Update
.mst Windows SDK Setup Transform Script
.ops Office Profile Settings File
.osd Application virtualized with Microsoft SoftGrid Sequencer
.pcd Visual Test (Microsoft)
.pif Windows Program Information File (Microsoft)
.pl Perl script file
.plg Developer Studio Build Log
.prf Windows System File
.prg Program File
.pst MS Exchange Address Book File, Outlook Personal Folder File (Microsoft)
.reg Registration Information/Key for W95/98, Registry Data File
.scf Windows Explorer Command
.scr Windows Screen Saver
.sct Windows Script Component, Foxpro Screen (Microsoft)
.shb Windows Shortcut into a Document
.shs Shell Scrap Object File
.ps1 Windows PowerShell
.ps1xml Windows PowerShell
.ps2 Windows PowerShell
.ps2xml Windows PowerShell
.psc1 Windows PowerShell
.psc2 Windows PowerShell
.tmp Temporary File/Folder
.url Internet Location
.vb VBScript File or Any VisualBasic Source
.vbe VBScript Encoded Script File
.vbp Visual Basic project file
.vbs VBScript Script File, Visual Basic for Applications Script
.vsmacros Visual Studio .NET Binary-based Macro Project (Microsoft)
.vsw Visio Workspace File (Microsoft)
.ws Windows Script File
.wsc Windows Script Component
.wsf Windows Script File
.wsh Windows Script Host Settings File
.xbap XAML browser application
.xnk Exchange Public Folder Shortcut