Does the POP service stops unexpectedly on your Exchange Server ?

"The POP service stops unexpectedly on your front-end Exchange 2000 Server or Exchange Server 2003 computer"

When the configuration of Microsoft Exchange 2000 Server or Microsoft Exchange Server 2003 computers as follows, the POP service on the front-end Exchange Server computer may stop unexpectedly (crash) when a back-end server fails over:
Then either Your Exchange Server computers are configured in a front-end/back-end (FE/BE) server configuration or Your back-end Exchange Server computers are installed on a Microsoft Windows 2000-based or on a Windows 2003-based server cluster.

This causes if connections from the front-end Exchange server to the back-end Exchange servers are not cleaned up correctly when the back-end Exchange server fails over.

The Hotfix for this particular issue is available from Microsoft
To get more details and Hotfix please follow the link below

Hotfix for POP service in Exchange Server