How to configure Outlook to block additional attachment file name extensions

This article describes how to configure Microsoft Outlook to block attachment file name extensions that Outlook does not block by default. If you use Outlook in a Microsoft Exchange environment, you can configure the server to block certain attachment file name extensions by using the Outlook E-mail Security Administrator Package.

Additionally, this article includes information about how to customize your security settings for different Outlook configurations with and without Exchange.

How to customize your security settings to block additional attachment file name extensions

The following methods describe how to customize your security settings for different Outlook configurations with and without Exchange.

How to block attachment file name extensions in an Exchange environment with the Outlook Security Administrator Package

If you have an Exchange environment that uses the Outlook Security Administrator Package and you want to add more attachment file name extensions that you want to block in your Outlook configuration, you can add more attachment file name extensions to the Level 1 file list. To do this, follow these steps:

1. Start Outlook with an account that has permissions to change the Outlook Security Form in the Outlook 10 Security Settings public folder.
2. In the folder list pane, locate the version-specific Outlook Security Settings public folder.
   
   Note For Microsoft Outlook 2000, the name of the public folder is Outlook Security Settings. For Microsoft Outlook 2002 and Microsoft Office Outlook 2003, the name of the public folder is Outlook 10 Security Settings.
3. Double-click Default Security Form.
4. Under Miscellaneous Attachment Settings, click to clear the Show level 1 attachments check box.
5. Under Level 1 File Extensions, type the attachment file name extensions that you want to block in the Add box.
   
   If you want to add more attachment file name extensions in the Add box, you can separate them with a semicolon. For example, if you want to block both the .zip and the .gif attachment file name extensions, type .zip; .gif
6. Click Close, and then click Yes to save your changes.
7. Repeat these steps for each Outlook Security Form that you have in the public folder for each security group that you want to add more attachment file name extensions to.

The next time that your users start Outlook, the new settings will be applied.

Note If you the Show Level 1 File Attachments check box from step 4 was already selected to allow all Level 1 attachment file name extensions types to appear in the e-mail message as an attachment, you must add the attachment file name extensions that you do not want to appear in the e-mail message as an attachment by following this one additional step:

• Under Level 1 File Extensions, locate the Remove box. In the Remove box, type the attachment file name extensions that you do not want to appear in the e-mail message as an attachment.
  
  If you want to add more attachment file name extensions in the Add box, you can separate them with a semicolon. For example, if you want to block both the .zip and the .gif attachment file name extensions, type .zip; .gif

For additional information about how to configure Outlook related security public folders in your Exchange environment , click the following article numbers to view the articles in the Microsoft Knowledge Base: Note Knowledge Base article 290499 also applies to to Outlook 2003.

How to block attachments in a non-Exchange environment

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: Use the information that is in this section if you are running Outlook in a non-Exchange environment and you want to block more attachment file name extensions than those that Outlook already blocks.

If you are using Outlook 2000, Microsoft Office 2000 Service Pack 3 (SP3) or later must be installed on your computer so that you can configure Outlook 2000 to block certain attachment file name extensions.

To obtain the latest service pack for Microsoft Office 2000, click the following article number to view the article in the Microsoft Knowledge Base: If you are using Outlook 2002, Microsoft Office XP Service Pack 1 (SP1) or later must be installed on your computer so that you can configure Outlook 2002 to block certain attachment file name extensions. To obtain the latest service pack for Microsoft Office XP, click the following article number to view the article in the Microsoft Knowledge Base:Outlook uses the Level1Add registry key to permit you to add additional attachment file name extensions types that you want to block.

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

For Outlook 2000

Follow these steps, and then quit Registry Editor:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following key in the registry:
   HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Outlook\Security
3. On the Edit menu, point to New, and then click String Value.
4. Type Level1Add, and then press ENTER.
5. On the Edit menu, click Modify.
6. Type <file_name_extensions>, and then click OK.

Notefile_name_extensions is a list of the attachment file name extensions. Each attachment file name extension is separated by a semicolon. For example, type .zip; .gif if you want to block both .zip and .gif files from appearing in the e-mail message as an attachment.

Outlook 2002

Follow these steps, and then quit Registry Editor:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following key in the registry:
   HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security
3. On the Edit menu, point to New, and then click String Value.
4. Type Level1Add, and then press ENTER.
5. On the Edit menu, click Modify.
6. Type <file_name_extensions>, and then click OK.

Notefile_name_extensions is a list of the attachment file name extensions. Each attachment file name extension is separated by a semicolon. For example, type .zip; .gif if you want to block both .zip and .gif files from appearing in the e-mail message as an attachment.

If Outlook 2002 does not behave differently after you add the Level1Add registry value, click the following article number to view the article in the Microsoft Knowledge Base:

Additionally, you can add additional attachment file name extensions types that you want blocked by using system policies to add the following registry key for Outlook:

Outlook 2003

Follow these steps, and then quit Registry Editor:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following key in the registry:
   HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security
3. On the Edit menu, point to New, and then click String Value.
4. Type Level1Add, and then press ENTER.
5. On the Edit menu, click Modify.
6. Type <file_name_extensions>, and then click OK.

Notefile_name_extensions is a list of the attachment file name extensions. Each attachment file name extension is separated by a semicolon. For example, type .zip; .gif if you want to block both .zip and .gif files from appearing in the e-mail message as an attachment.

For more information about Outlook 2000 and Outlook 2002 security, see the Microsoft Office Resource Kit. To do so, visit the following Microsoft Web site: For more information about Outlook 2003 security, see the Microsoft Office 2003 Resource Kit. To do so, visit the following Microsoft Web site: