Topic Last Modified: 2005-11-18

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


If the Exchange Server Analyzer finds the CheckPop3Tail value present and configured with a value 1, a non-default configuration message is displayed.

Internet Engineering Task Force (IETF) Request for Comments (RFC) 1939 ( specifies a termination sequence of CRLF for POP3 messages. In Exchange parlance, the CRLF sequence is referred to as a POP3Tail. If a POP3 client, such as Microsoft Office Outlook® 2003 or Microsoft Outlook Express, encounters a malformed message with an incorrect POP3Tail (for example, a missing CRLF), it can stop responding and fail to download all the messages that are in the Inbox. The CheckPop3Tail registry value represents a configuration opportunity for administrators to instruct the Microsoft Exchange POP3 service to check the POP3Tail of each POP3 message, and add the correct termination sequence if it is missing.

This setting will correct malformed messages and enable the POP3 client to download all the messages in the user's Inbox; however, it will also cause slight performance degradation as each message will be checked for a proper POP3Tail.

If you want, you can use the procedure below to remove the CheckPop3Tail registry value.

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 delete the CheckPop3Tail registry value

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

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

  3. Delete the value called CheckPop3Tail.

  4. Close 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 the use of the CheckPop3Tail registry value, see the Knowledge Base article 816896, "XCCC: POP3 Client Stops Responding (Hangs) or Times Out When You Try to Download Messages" (