Unblocking attachments in Outlook

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How can you get an email attachment that Outlook for Windows has blocked?

Outlook will automatically block email attachments with certain extensions.  We’ve copied the full list of blocked extension below.  Developers and IT people are the most likely to get frustrated by Outlook file blocks.

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In many cases the blocked file is really plain text code or script which could be resent within an email message body instead of an attachment.  The receiver just selects part of the message and makes a new file.

Here’s some of the file types that you might want to get past Outlook with some comments on alternative ways to send the file.

.asp   an Active Server Page, commonly used on web sites.  A plain text file.The more recent .aspx equivalent is not blocked.

.cer, crt Internet certificate.  These are usually delivered by SSL providers via a .ZIP file.

.cmd  or .bat    Windows /DOS command file.  These are plain text and usually short so they can be sent in a message body and easily recreated.

.js  Javascript source code. Again, this is plain text and could be send in a message body instead.

.pl  Perl script.  Another plain text file.

.mdb .mda and other MS Access files.  Use ZIP instead (most compress into a much smaller file).

.ps1 and other PowerShell scripts.  Use plain text instead.

.reg  – more plain text

.url a Internet link, put in a message body instead.

Most of these are blocked for good reason.  Under no circumstances should you open a .exe attachment even from someone you trust.

But sometimes you’ll get an email with attachment that you need.  How to bypass the Outlook block?

The easiest option is to ask the sender to resend the files in a different format (like ZIP or RAR), to a different email account or via an online file share. But assuming those options aren’t available.

WARNING:  use any attachment you get after unblocking with extreme caution.  Microsoft hasn’t blocked these attachments to be annoying, they are trying to protect their customers.

Make sure that the email attachment comes from the genuine sender and it’s not a spoofed email that the sender has no clue about.

You can’t direct change what Microsoft calls the ‘Level 1’ block list for Outlook attachments but you can manually exclude an extension from the current list.

The Outlook attachment blocks can be removed in the Registry at:

HKEY_CURRENT_USER\Software\Microsoft\Office\<version>\Outlook\Security

The <version> of Outlook is

  • Outlook 2016 16.0
  • Outlook 2013 15.0
  • Outlook 2010 14.0
  • Outlook 2007 12.0
  • Outlook 2003 11.0
  • Outlook 2002 (XP) 10.0
  • Outlook 2000 9.0

For Outlook 2016 it’s

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Security

Now add a String value  Level1Remove 

The data is a list of extensions you want UNblocked with a dot/period and a semi-colon to separate.

To Unblock just Access .MDB files  use   .mdb 

To Unblock .mdb and .bat files use  .mdb;.bat

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After a registry change, restart Outlook and the blocked attachment is now available.

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If you’ve made the registry change just to access a single attachment.  Save the attachment to your computer (and check it for nasties) then remove the registry entry.

If you need to unblock occasionally, rename the key to disable it. That makes it easy to quickly restore in the future.

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Outlook will ignore a registry entry with a name it doesn’t recognize.

Here’s a list of blocked attachments, as advised by Microsoft.  There’s a search field at the top (depending on your browser).

File extensionFile type
.adeMicrosoft Access project extension
.adpMicrosoft Access project
.appApplication file
.aspActive server page
.basMicrosoft Visual Basic class module
.batBatch file
.cerInternet Security Certificate file
.chmCompiled HTML Help file
.cmdDOS CP/M command file, Microsoft Windows NT command script
.cntWindows Help contents file
.comMicrosoft MS_DOS program
.cplControl Panel extension
.crtSecurity certificate
.cshScript file
.derDER Encoded X509 certificate file
.exeExecutable file
.fxpMicrosoft Visual FoxPro compiled program
.gadgetWindows Gadget
.grpWindows program group file
.hlpHelp file
.hpjHelp project file
.htaHTML program
.infInformation or setup file
.insInternet Naming Service
.ispInternet Communication settings
.itsInternet Document Set file
.jarJAVA archive file
.jsJavaScript source code
.jseJScript Encoded script file
.kshUNIX Shell script file
.lnkWindows shortcut
.madMicrosoft Access module shortcut
.mafMicrosoft Access shortcut
.magMicrosoft Access diagram shortcut
.mamMicrosoft Access macro shortcut
.maqMicrosoft Access query shortcut
.marMicrosoft Access report shortcut
.masMicrosoft Access stored procedures
.matMicrosoft Access table shortcut
.mauMedia attachment unit
.mavMicrosoft Access view shortcut
.mawMicrosoft Access data access page
.mcfManifest configuration file
.mdaMicrosoft Access add-in program
.mdbMicrosoft Access program
.mdeMicrosoft Access MDE database file
.mdtMicrosoft Access data file
.mdwMicrosoft Access workgroup
.mdzMicrosoft Access wizard program
.mscMicrosoft Common Console document
.mshWindows PowerShell script helper
.msh1Windows PowerShell script helper
.msh2Windows PowerShell script helper
.mshxmlWindows PowerShell script helper
.msh1xmlWindows PowerShell script helper
.msh2xmlWindows PowerShell script helper
.msiWindows Installer package
.mspWindows Installer update package file
.mstVisual Test source file
.opsMicrosoft Office profile settings file
.osdOpen software description file
.pcdMicrosoft Visual Test compiled script
.pifWindows program information file
.plPerl script file
.plgDeveloper Studio build log
.prfOutlook profile file
.prgProgram source file
.ps1Windows PowerShell
.ps1xmlWindows PowerShell
.ps2Windows PowerShell
.ps2xmlWindows PowerShell
.psc1Windows PowerShell
.psc2Windows PowerShell
.pstMicrosoft Outlook personal folder file
.regRegistration entries, Registry data file
.scfWindows Explorer command file
.scrWindows screen saver
.sctWindows script component
.shbWindows shortcut to a document
.shsShell Scrap object file
.tmpTemporary file or folder
.urlUniform Resource Locator (Internet shortcut)
.vbMicrosoft Visual Basic Scripting Edition (VBScript) file
.vbeVBScript Encoded script file
.vbpVisual Basic project file
.vbsVBScript script file, Visual Basic for Applications script file
.vsmacrosMicrosoft Visual Studio .NET binary-based macro project file
.vswMicrosoft Visio workspace file
.wsWindows script file
.wscWindows script component
.wsfWindows script file
.wshWindows Script Host settings file
.xbapXAML browser application
.xnkMicrosoft Exchange public folder shortcut
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