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Block Additional File Types in Outlook

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› Outlook › Block Additional File Types in Outlook

Last reviewed on February 13, 2018     6 Comments

August 4, 2011 by Diane Poremsky 6 Comments

While many people want to unblock file types that are blocked by Outlook's security, with recent viruses using the zip file type to propagate, you may want to block zips to prevent someone from opening zips accidentally.

Choose between two options:

Level1Remove -- slow down access to the zip by forcing users to save them to the hard drive before opening them. With this enabled, users will be presented with a dialog like the one shown here when they double click on an attachment.

Attachment security dialog

Level1Add -- treat *.zips like *.exes to completely block access to them.

Level1Remove

To Add file types to Level1Remove key:

  1. Press windows key + R to open the run command. Type Regedit and press enter to open the registry editor.
  2. Browse to the appropriate key for your version of Outlook
  3. Add a new String value named Level1Remove.
  4. For the value for Level1Remove, enter a semicolon-delimited list of file extensions. For example, entering this: .zip;.mdb;.url; would force you to save Zip file type and unblock Microsoft Access files and Internet shortcuts.

Outlook 2016

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Security
String: Level1Remove
Value: .ext;.ext; format

Outlook 2013

HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Security
String: Level1Remove
Value: .ext;.ext; format

Outlook 2010

HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security
String: Level1Remove
Value: .ext;.ext; format

Outlook 2007

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security
String: Level1Remove
Value: .ext;.ext; format

Outlook 2003

HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security
String: Level1Remove
Value: .ext;.ext; format

Outlook 2002

HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security
String: Level1Remove
Value: .ext;.ext; format

Outlook 2000

HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Outlook\Security
String: Level1Remove
Value: .ext;.ext; format

Level1Add

To Block file types using the Level1Add key:

To add additional attachment file name extensions types that you want blocked, you must add the Level1Add key to the registry. To do this, follow these steps.

  1. Run Regedit browse to the appropriate registry key for your version of Outlook.
  2. Add a new string value named Level1Add.
  3. For the value for Level1Add, enter a semicolon-delimited list of file extensions. For example, entering .zip would treat the Zip file type like exe's and block access to them.

Outlook 2016

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Security
String: Level1Add
Value: .zip;.pdf; format

Outlook 2013

HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Security
String: Level1Add
Value: .zip;.pdf; format

Outlook 2010

HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security
String: Level1Add
Value: .zip;.pdf; format

Outlook 2007

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security
String: Level1Add
Value: .zip;.pdf; format

Outlook 2003

HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security
String: Level1Add
Value: .zip;.pdf; format

Outlook 2002

HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security
String: Level1Add
Value: .zip;.pdf; format

Outlook 2000

HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Outlook\Security
String: Level1Add
Value: .zip;.pdf; format

 

Tools

Attachment Options

COM add-in by Outlook MVP Ken Slovak that adds an Attachment Security Options page to the Tools, Options dialog in Outlook 2000 SP3 or higher to allow you to manage which file attachments are blocked. New version adds support for the .gadget extension for Outlook 2003 SP3 and Outlook 2007 SP1. It also adds detection for those SP levels. Shareware. Version 1.9.6

Attachment Security for Microsoft Outlook

"Outlook blocked access to the following potentially unsafe attachment ..." If you get this message when attempting to access an Outlook email attachment you'll want to install Attachment Security for Outlook; a free program for unlocking attachments blocked by Outlook. Attachment Security for Microsoft Outlook is a free and easy to use software program that allows you to open attachments blocked by Microsoft Outlook e-mail security.

CodeTwo Outlook WarningDoctor

CodeTwo Outlook WarningDoctor removes the security warnings that appear when sending mail or performing other actions recognized by Microsoft as a "risky" (for example, when you try to read some data using the Outlook or CDO API #. Especially useful for designers of macros, Visual Basic, and programmers of other scripting languages that use the object model.Outlook 2000 and up, including Outlook 2010 64bit.

Outlook Security Manager

Developers can use this to avoid the security prompts in Outlook.

More Information

  • Outlook Email Security Update
  • Protecting Outlook against Viruses
  • How to configure Outlook to block additional attachment file name extensions

Block Additional File Types in Outlook was last modified: February 13th, 2018 by Diane Poremsky

Related Posts:

  • Opening .exe Attachments and Outlook E-mail Security
  • Embedded Objects are Blocked in Outlook Items
  • Block Macros in Office 2013/2016
  • Outlook Folder Homepages are missing

About Diane Poremsky

A Microsoft Outlook Most Valuable Professional (MVP) since 1999, Diane is the author of several books, including Outlook 2013 Absolute Beginners Book. She also created video training CDs and online training classes for Microsoft Outlook. You can find her helping people online in Outlook Forums as well as in the Microsoft Answers and TechNet forums.

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kevin
kevin

just delete the Level 1 key and then restart outlook...worked for me.

Vote Up00Vote Down Reply
April 25, 2018 3:13 pm
Diane Poremsky
Diane Poremsky

The level1 key shouldn't exist by default, so yeah, if you (or an application) added it, delete it.

Vote Up00Vote Down Reply
April 25, 2018 11:57 pm
Sean
Sean

FYI, there is a THIRD level for extension types which will allow you to avoid saving the file first (at least for Outlook 2007) before opening it: OtherAdd
The meaning of the three levels are: Level1=Fully blocked, Level2=Prompt to Save, and Other=Prompt to open or save.
The way Outlook is supposed to work is that any extension not in Level1 and not in Level2 should fall to Other. That's not always true.
When creating a registry key for an extension, keep it simple and only use the level you wish to add your extension into.
In other words, don't use a Level1Remove and a Level2Remove hoping to get the desired extension added to the Other list; just use a single OtherAdd registry entry.
Lastly, when Outlook compares an attachment extension to the lists from the registry, IT IS CASE SENSITIVE! Therefore, say you want to allow Outlook to immediately Open the Excel 2003 .xls extension: Create a single key for OtherAdd and cover your bases by using the value of .xls;.xlS;.xLs;.xLS;.Xls;.XlS;.XLs;.XLS; (Also: REMEMBER TO END THE STRING WITH A SEMI-COLON!)

Hope that helps someone,
Sean

Vote Up00Vote Down Reply
July 13, 2017 6:59 pm
Diane Poremsky
Diane Poremsky

There is not actually an "other list" - it's just all of the extensions not blocked as unsafe. Unless things changed in a recent update, the extensions are NOT case sensitive - you should use lower case.

FWIW, Office files shouldn't be blocked. If the check box on the open or save dialog is turned off, open outlook using run as administrator and open the file - you'll be able to tick the checkbox to never ask again. More info: https://www.slipstick.com/problems/disable-always-ask-before-opening-dialog/

Vote Up0-1Vote Down Reply
July 13, 2017 10:56 pm
blip.blip
blip.blip

this page keeps re-loading in internet explorer. please fix

Vote Up1-1Vote Down Reply
December 16, 2013 4:06 pm
Diane Poremsky

What version of IE are you using?

Vote Up1-1Vote Down Reply
December 16, 2013 4:19 pm

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