You create an Outlook profile for a Post Office Protocol 3 (POP3) user in a Microsoft Exchange Server 2010 environment.
You configure Outlook to download POP3 email messages to an Exchange Server 2010 mailbox. For example, you enable the Leave a copy of messages on the server setting when you configure the POP3 account.
In this scenario, Outlook downloads all POP3 email messages every time it starts. Therefore, duplicated POP3 email messages are in the mailbox.
Note You expect Outlook to download these messages only once.
The issue occurs because the Microsoft Exchange RPC Client Access service on the Exchange Server 2010 Client Access Server (CAS) role incorrectly overwrites the long attachment file name to an 8.3 short name. Because of this issue, Outlook cannot determine which POP3 messages were downloaded. Therefore, Outlook downloads all POP3 messages every time it starts.
To resolve this issue, install the following update rollup:
2579150 Description of Update Rollup 4 for Exchange Server 2010 Service Pack 1
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.