SYMPTOMS
You may experience this problem if you applied version 5.0.1458.10 of
Store.exe for Microsoft Exchange version 5.0, to resolve the problem
described in the following article in the Microsoft Knowledge Base:
166562
XFOR: Store.exe GPFs When POP3 Client Submits Bad Message Header
You may have POP3 clients that cannot download all of their mail.
Typically, they will see the following errors in the event log:
12802
MSExchange Pop3
Error 0x8004010f during stream configuration
11310
MSExchange Pop3
The following error occurred: The requested item could not be found.
If you telnet to port 110 and attempt to retrieve the message, the
following error message appears:
The requested item could not be found.
Not all messages are affected, only some. Usually the rejected messages are
all of the same type, such as Microsoft Mail messages, or messages with
attachments, and so on.