Consider the following scenario:
- You have a computer that is running Microsoft Outlook 2013.
- You access the Internet by using a proxy server that is configured to use basic authentication.
- You use Outlook 2013 to open an HTML-formatted email message.
- The HTML-formatted email message contains an HTTP reference to an image that requires proxy authentication.
To resolve this issue, follow these steps:
- Click Start, click Run, type regedit in the Open box, and then click OK.
- Locate and then select the following registry subkey:HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common
- On the Edit menu, point to New, and then click DWORD (32-bit) Value.
- Type AllowImageProxyAuth, and then press Enter.
- In the Details pane, right-click AllowImageProxyAuth, and then click Modify.
- In the Value data box, type 1 or 2, and then click OK.
- Exit Registry Editor.
- If you set the value to 1 in step 6, you are prompted for authentication one time per Outlook session in the scenario that is described in the "Symptoms" section. If you cancel the authentication request, you are not prompted again during that Outlook session. This option introduces a small volume of network overhead per Outlook session.
- If you set the value to 2 in step 6, you are prompted for authentication when it is required. Typically you are prompted for authentication one time per Outlook session. However, in some scenarios, you may be prompted multiple times. For example, if you cancel the authentication request for one image, you are prompted again for the next image that requires proxy authentication. This option introduces additional network overhead for each downloaded image. If an email message contains multiple images, the additional network overhead may cause slow performance in Outlook.
- If the value in step 6 is nonexistent, or if you set the value to 0, you are not prompted for authentication, and the image might not be displayed.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.