SYMPTOMS

When you use Windows Vista to try to access a Web site or email, the Web site or email server sends data very slowly or drops the data completely. It takes a very long time to download an e-mail message from a POP3 server in Microsoft Office Outlook 2007. For example, when you download a 1-megabyte (MB) message, the download process may take one hour.

CAUSE

This problem occurs if a network hardware device, such as a router, does not support TCP Window Scaling. TCP Window Scaling is a new Windows Vista feature. By default, Windows Vista supposedly supports RFC 1323 and supports a Windows Scaling factor of 8. This issue occurs when a Web site or email server supposedly does not fully support RFC 1323 or when a Web site or email server supposedly does not support the default scaling factor.

WORKAROUND

To work around this issue, disable the Windows Scaling factor. To disable the Windows Scaling factor, follow these steps:

1. Click Start, click All Programs, and then click Accessories.
2. Right-click Command Prompt, and then click Run as administrator.
3. At the prompt in the Administrator: Command Prompt window, type the following command, and then press ENTER:

   netsh interface tcp set global autotuninglevel=disable

4. Restart your computer for the changes to take effect.