Outlook – Unblocking Blocked Attachments

Below is a list of file extensions automatically blocked by Outlook. Why are they blocked? Well attachments with the file extensions listed below are known to potentially contain a virus. Now, not every attachment sent to you with or without one of the extensions on the hit list contains a virus but Outlook does not know which contains what so they are all blocked. From a security point of view this is good, from a practical point of view not so good. If you are security minded you will scan all emails and attachments anyway, if your AV program doesn’t do it automatically. If you are not security minded don’t read anymore of this article and don’t unblock attachments.

This tip involves a registry change so use caution and create a system restore point before proceeding and/or backup your registry.

Close Outlook if it is running in the tray.
Open your registry editor by typing regedit in the Run/Search box on XP, Vista or Se7en


or by typing regedit on the Start Screen of Windows 8 and pressing Enter.

Where you need to navigate to is dependent on your version of Outlook, but its straight forward enough.
Click on HKEY_CURRENT_USER then Software and then Microsoft.
Now click on Office then your version number followed by Outlook and finally Security.

For Outlook 2003 your version number will be 11.0, for 2007 the version is 12.0, for 2010 the version is 14.0 and for 2013 it is version 15.0.
Right click in the right hand pane and select New then String Value.

Name the String Level1Remove and click OK.
Double click on the string and you need to add the extensions you want to unblock including the preceding dot, if you want to unblock more than one file type then you must separate them with a semi-colon as such: .exe;.lnk;.app and so forth.

OK your way out of the registry editor and your chosen extensions are unblocked.
As I previously said if you do unblock any of the extensions below make sure you have your email attachments scanned.

Blocked Extensions
.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
.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)
.its     Internet Document Set, Internet Translation
.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)
.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)
.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
.xnk     Exchange Public Folder Shortcut

To block the extensions again just delete the string Level1Remove.

2 thoughts on “Outlook – Unblocking Blocked Attachments”

  1. Thank you, Alan Wade,
    Most informative!
    So, if one was to decide to unblock all of the extensions shown on the above list; would the following be the set that they would want to add to the newly created registry String (named ‘Level1Remove’)?
    Cheers, RandiO.

  2. Thanks and yes, just seperate each of the extension types with a semi-colon.

Comments are closed.

Exit mobile version


Get great content like this delivered to your inbox!

It's free, convenient, and delivered right to your inbox! We do not spam and we will not share your address. Period!