It takes much longer than expected to download an e-mail message from a POP3 server in Outlook 2007

When you try to download an e-mail message from a POP3 server in Microsoft Office Outlook 2007, it takes much longer than expected. For example, when you download a 1-megabyte (MB) message, the download process may take as long as one hour.

Additionally, when you send e-mail messages by using the SMTP server of an Internet service provider (ISP), the connection may time out. When this problem occurs, you may receive the following error message: 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.

This article helps you fix the problem. To have us fix this problem for you, go to the “Fix it for me” section. If you would rather fix this problem yourself, go to the “Let me fix it myself” section.

To fix this problem automatically, click the Fix this problem link. Then, click Run in the File Download dialog box, and follow the steps in this wizard.

Fix this problem
Microsoft Fix it 50056

Notes

• This wizard may be in English only; however, the automatic fix also works for other language versions of Windows.
• If you are not on the computer that has the problem, you can save the automatic fix to a flash drive or to a CD, and then you can run it on the computer that has the problem.

Now go to the "Did this fix the problem?" section.

To determine whether this problem is caused by a network hardware device that does not support TCP Window Scaling, follow these steps:

1. Click Start
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   , click All Programs, and then click Accessories.
2. Right-click Command Prompt, and then click Run as Administrator.
   
   
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   If you are prompted for an administrator password or for confirmation, type the password, or click Continue.
3. At the command prompt, type the following command, and then press ENTER:
   netsh interface tcp set global autotuninglevel=disabled
4. Close the Command Prompt window.
5. Restart the computer.
6. Start Outlook. If the problem is fixed, you can either keep the value for the autoTuningLevel parameter as disabled or isolate the hardware that does not support TCP Window Scaling. You can also set the autoTuningLevel parameter to other values, as described in the "More Information" section.

Now go to the "Did this fix the problem?" section.

Check whether the problem is fixed. If the problem is fixed, you are finished with this article. If the problem is not fixed, you can contact support (http://support.microsoft.com/contactus) .

To see the current configuration for the autoTuningLevel parameter, follow these steps:

1. Click Start
   Collapse this imageExpand this image

   
   , click All Programs, and then click Accessories.
2. Right-click Command Prompt, and then click Run as Administrator.
   
   
   Collapse this imageExpand this image

   
   If you are prompted for an administrator password or for confirmation, type the password, or click Continue.
3. At the command prompt, type the following command, and then press ENTER:
   netsh interface tcp show global
   The value for the autoTuningLevel parameter is listed as Receive Window Auto-Tuning Level.

The following list includes all possible values for the autoTuningLevel parameter:

• disabled
  Sets the receive window at the default value.
• highlyrestricted
  Lets the receive window grow beyond the default value, but does so very conservatively.
• restricted
  Lets the receive window grow beyond the default value, but limits such growth in some scenarios.
• normal
  Lets the receive window grow to accommodate most scenarios.
• experimental
  Lets the receive window grow to accommodate extreme scenarios.
  
  Note The experimental value may decrease performance in common scenarios. This value should be used only for research purposes.

The TCP receive window size is the maximum amount of received data in bytes that can be buffered at the same time on the receiving side of a connection. The sending host can send only that amount of data before waiting for an acknowledgement and for a "receive window" update from the receiving host.

The TCP/IP stack in Windows Vista tunes itself in most environments by using larger default window sizes than in earlier versions of Windows. Instead of using a hard-coded default receive window size, TCP automatically adjusts the window size to increase the percentage of full-sized TCP segments that are used during bulk data transmission. This helps limit the number of segments that are sent when large sets of data are transmitted.

When auto-tuning is enabled in Windows Vista, Receive the Window Auto-Tuning feature continually determines the optimal true receive window size by measuring the bandwidth delay product and the application retrieve rate. Then, Receive Window Auto-Tuning adjusts the maximum receive window size based on the changing network conditions.

For more information about the Next Generation TCP/IP stack that includes Receive Window Auto-Tuning, visit the following Microsoft Web site:For more information about Windows TCP implementation features, visit the following Microsoft Web site: For more information about TCP receive window size and about window scaling, visit the following Microsoft Web site:For more information about RFC 1323, visit the following Internet Engineering Task Force Web site: Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.