MSExchangePOP3 service crashes in an Exchange Server 2007 environment

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Symptoms

When a client issues a QUIT�command to end a POP3 session, the MSExchangePOP3 service crashes occasionally on a Microsoft Exchange Server 2007 Client Access server. Additionally, the following event is logged in the Application log:

Log Name: Application
Source: Application Error
Date: Date
Event ID: 1000
Task Category: (100)
Level: Error
Keywords: Classic
User: N/A
Computer: Computer
Description:
Faulting application name: Microsoft.Exchange.Pop3.exe, version: version, time stamp: time stamp
Faulting module name: unknown, version: 0.0.0.0, time stamp: 0x00000000
Exception code: 0xc0000005
Fault offset: offset
Faulting process id: process id
Faulting application start time: start time
Faulting application path: C:\Program Files\Microsoft\Exchange Server\ClientAccess\PopImap\Microsoft.Exchange.Pop3.exe
Faulting module path: unknown
Report Id: report id

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Cause

This issue occurs because of a NullReferenceException exception when the Exchange server processes a POP3 session quit command. The NullReferenceException exception is caused by a race condition during the POP3 session object disposal. In this race condition, the VirtualServer object is set to NULL before it is used. Therefore, the MSExchangePOP3 service crashes.

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