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Missing POP3 email 'tails' may torment Microsoft Outlook

Microsoft Outlook clients may hang when trying to retrieve POP3 email from an Exchange server if any of the POP3 messages are not formatted with a proper termination sequence or "tail."

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Microsoft Outlook (and Outlook Express) users who use Exchange Server to receive POP3 email have occasionally reported a problem where Microsoft Outlook hangs in the middle of message retrieval.

The problem is usually related to a given message in the queue that can't be downloaded correctly and needs to be deleted. Unfortunately, this troublesome email isn't discernibly different from other messages in most cases.

The issue may be the lack of a proper termination sequence or "tail" on a particular POP3 email message. RFC 1939 (the POP3 protocol specification) dictates that all email messages must end with a pair of CR+LF characters.

If a POP3 email message doesn't have the correct termination sequence appended to it, the email client, which is simply following POP3 protocol, can't tell the end of one message from the beginning of another -- so it gets stuck downloading what it thinks is the same message in perpetuity.

If you experience this issue because of a fair number of incoming malformed messages, or you want to protect against it proactively, you can set Exchange Server to enforce the presence of a termination sequence on all messages downloaded through POP3.

  1. Open the registry on the Microsoft Exchange machine that serves as the POP3 host and navigate to:

    HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\POP3Svc\Parameters.

  2. Create (or edit) a new DWORD value named CheckPop3Tail, and set it to 1 (hex or decimal).

  3. Stop and restart the POP3SVC service to make sure the changes take effect.

Note: The above procedure might cause a slight decrease in performance for Exchange servers with a lot of POP3 traffic, but any hardware capable of running Exchange 2000 or Exchange 2003 well will probably not evince any slowdown.

About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter.


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POP3Svc does not appear in the Registry list.
—Malcolm P.

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This entry would only be present if you have the POP3 service installed in the first place. If you're using some other means to route email into Exchange via POP3, it wouldn't be present.

Microsoft has some information about this service.
—Serdar Yegulalp, tip author

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Related information from SearchExchange.com:

  • FAQ: Exchange Server and POP3
  • Tip: A primer on messaging standards -- SMTP, POP and IMAP
  • Ask the Expert: How to automatically forward Exchange email to a POP3 account
  • Reference Center: Microsoft Outlook tips and resources

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