These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk. If a Security registry key does not exist, create a new key. To do this, follow these steps:. On the Edit menu, point to New , and then click Key. When you send an encrypted email message to a recipient, Outlook uses the recipient's certificate to secure the message. If the email address of the contact or recipient is different from the email address that is specified in the recipient's certificate, you receive the following warning:.
Encryption Problems Microsoft Outlook had problems encrypting this message because the following recipients had missing or invalid certificates, or conflicting or unsupported encryption capabilities: recipient name Continue will encrypt and send the message but the listed recipients may not be able to read it.
Send Unencrypted Continue Cancel To prevent Outlook from displaying this warning message, apply the registry change described in the Resolution section of this article. If you do not use Outlook with an Exchange server or if the Exchange server administrator lets users change the Outlook attachment security behavior, use method 1: "Customize attachment security behavior.
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:.
Follow these steps to modify the registry and change Outlook's attachment security behavior. Click Start , and then click Run.
Verify that the following registry key for your version of Outlook exists. Microsoft Office Outlook If the registry key does not exist, follow these steps to create it:. Under Edit , click New , and then click Key. For Outlook , type For Outlook , type 9. Under Edit , click New , and then click String Value. When you start Outlook, open the file types you specified in the registry.
Note We recommend that you enable only the file types that you have to have. If you rarely receive a particular file type, we recommend that you give Outlook temporary access to the file type that is in question.
Then, reconfigure Outlook to block the file type by undoing the changes to the registry. For more information about how you can configure Outlook to block attachment file name extensions that Outlook does not block by default, click the following article number to view the article in the Microsoft Knowledge Base:.
If you run Outlook in an Exchange environment, the Exchange server administrator can change the default attachment security behavior. For more information about how to configure Outlook in an Exchange environment, click the following article numbers to view the articles in the Microsoft Knowledge Base:.
Attachments are divided into three groups based on their file name extension or file type. Outlook handles each group in a specific way. The unsafe category represents any file name extension that may have script or code associated with it. You cannot open any attachment that has an unsafe file name extension. For a list of the unsafe file name extensions, see this Office support page.
Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, see Description of the Microsoft Windows registry. When you send a secure message in Microsoft Outlook , Microsoft Outlook , Microsoft Office Outlook , Microsoft Office Outlook , Microsoft Outlook , or in Microsoft Outlook , you may need to use a certificate that does not match your e-mail address.
This article describes how to turn off e-mail matching for certificates. You can turn off e-mail address matching for certificates by editing your registry. To do this, follow these steps, as appropriate for the version of Outlook that you are running.
Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. 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. 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:.
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:.
If you are using Outlook , Microsoft Office Service Pack 3 SP3 or later must be installed on your computer so that you can configure Outlook to block certain attachment file name extensions. To obtain the latest service pack for Microsoft Office , click the following article number to view the article in the Microsoft Knowledge Base:. To obtain the latest service pack for Microsoft Office XP, click the following article number to view the article in the Microsoft Knowledge Base:.
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. Click Start , click Run , type regedit, and then click OK.
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