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.

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 and newer

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

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 and newer

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

File types blocked in Outlook

Below is a list of file extensions blocked in Outlook.