Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool reads the following registry entry to determine if the following registry value exists:


If the Exchange Server Analyzer finds the MaxBufferSize value present and configured with any numeric value greater than 32768, a warning is displayed.

The MaxBufferSize registry value is used in an Exchange front-end/back-end topology. It defines the TCP/IP buffer size between front-end servers and back-end servers. The default buffer size is 1 kilobyte (KB). On networks with high latency, adjusting the MaxBufferSize value can improve performance for POP3 clients.

When setting the TCP/IP buffer size with the MaxBufferSize registry value, you should always set the buffer size in multiples of 1,024. It is recommended that you test your front-end/back-end server configuration performance with the following buffer sizes:

When using this registry entry, it must be set to at least 1,024. It is recommended that you do not set the MaxBufferSize registry entry to a value greater than 32,768. However, you may notice increased performance with a buffer size value of 65,535, depending on your network conditions. A larger buffer size uses more memory on the Exchange Server computer and may decrease the number of users who can access the front-end server. While there is no limit to the maximum value that you can use for the MaxBufferSize registry value, you may experience unstable performance and memory issues if you assign too great a value to this registry entry.

To use the MaxBufferSize registry value, you must be running Exchange 2000 Server Service Pack 2 or later.

If the MaxBufferSize registry value is set too low, performance will not improve and the Exchange Server Analyzer will display an error message, as described in POP3 MaxBufferSize value is too low. If the MaxBufferSize registry value is set too high, system instability could result and the Exchange Server Analyzer will display a message, as described in this article.

This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore the registry if a problem occurs. For information about how to restore the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.

To correct this error

  1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

  2. Navigate to: HKLM\System\CurrentControlSet\Services\POP3Svc\Parameters

  3. Create a new DWORD value called MaxBufferSize.

  4. Double-click the MaxBufferSize value and set it to the new buffer size (in bytes). For example, you can enter 8192 to set it to 8,192 bytes.

  5. Exit the registry editor and restart the Microsoft Exchange POP3 service for the change to take effect.

Before you edit the registry, and for information about how to edit the registry, see the Microsoft Knowledge Base article 256986, "Description of the Microsoft Windows Registry" (

For more information about when and how to use the MaxBufferSize registry value, see the Knowledge Base article 823857, "XADM: IMAP4 and POP3 Performance Is Slow Between Front-End and Back-End Servers" (